Processes for pretreating and purifying a cellulosic material

ABSTRACT

A process for treating a cellulosic material comprising pretreating the cellulosic material and then extracting the cellulosic material with an extractant to selectively extract hemicellulose therefrom and separating the extracted hemicellulose to form a cellulosic product comprising less hemicellulose than the cellulosic material. The extractant comprises a cellulose solvent and a co-solvent. The cellulosic product advantageously retains its cellulosic fiber morphology. The processes involve separating and recovering the hemicellulose and separating and recycling various process streams employed in the process.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional No. 62/033,442, filed Aug. 5, 2014, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for obtaining a cellulosic product from a raw cellulosic material. In particular, the present invention relates to processes for converting raw cellulosic materials into pulp, pretreating the pulp, and then purifying the pretreated pulp to produce purified pulp comprising cellulose and having reduced hemicellulose content.

BACKGROUND OF THE INVENTION

Cellulose is typically obtained from wood pulp and cotton and may be further modified to create derivatives including regenerated cellulose, cellulose ethers, cellulose esters and cellulose nitrate, among others. Cellulose derivatives have a variety of commercial uses. For example, cellulose acetate is the acetate ester of cellulose and is used for a variety of products, including textiles (e.g., linings, blouses, dresses, wedding and party attire, home furnishings, draperies, upholstery and slip covers), industrial uses (e.g., cigarette and other filters for tobacco products, and ink reservoirs for fiber tip pens, decking lumber), high absorbency products (e.g., diapers, sanitary napkins, and surgical products), thermoplastic products (e.g., film applications, plastic instruments, and tape), cosmetic and pharmaceutical (extended capsule/tablet release agents and encapsulating agent), medicinal (hypoallergenic surgical products) and others.

High purity α-cellulose is commonly required as a starting material to make cellulose derivatives, such as cellulose acetate. Acetate-grade pulps are specialty raw materials produced in commercial pulp processes, but the cost for such pulps is high. Commercial paper grade pulps contain less than 90% α-cellulose and are potential crude cellulosic sources for making cellulose derivatives. Paper grade pulp contains a high amount of impurities, such as hemicellulose, rendering it incompatible with certain industrial uses, such as making cellulose acetate flake or tow.

Zhou et al. discusses the use of dimethyldioxirane (DMDO), a pulp bleaching agent, to treat birch pulp and obtain acetate-grade pulp. However, DMDO is not currently commercially available due to its instability. Therefore, it is not an ideal solvent for producing large quantities of high α-cellulose content pulp. Zhou et al. “Acetate-grade pulp from birch,” BioResources, (2010), 5(3), 1779-1778.

Studies have been done regarding the treatment of biomass to form biofuels. Specifically, it is known that various ionic liquids can be used to dissolve cellulosic material. S. Zhu et al. in Green Chem. 2006, 8, pp. 325-327, describe the possibility of dissolving cellulose in ionic liquids and recovering it by addition of suitable precipitating agents such as water, ethanol, or acetone.

Others have used ionic liquids to break down the cellulosic materials to make biofuels by way of glucose. For example, U.S. Pub. No. 2010/0112646 discloses a process for preparing glucose from a cellulose material, in which a cellulose-comprising starting material is provided and treated with a liquid treatment medium comprising an ionic liquid and an enzyme. Similarly, U.S. Pub. No. 2010/0081798 discloses a process for preparing glucose from a material containing ligno-cellulose, in which the material is first treated with an ionic liquid and then subjected to enzymatic hydrolysis. U.S. Pub. No. 2010/0081798 describes obtaining glucose by treating a material containing ligno-cellulose with an ionic liquid and subjecting same to an enzymatic hydrolysis and fermentation. However, in order to turn cellulose containing materials into glucose, the methods disclosed in these references result in breaking down the cellulose molecules, making them unsuitable for use as starting materials to make cellulose derivatives.

U.S. Pat. No. 7,828,936 describes a method for dissolving cellulose in which the cellulose based raw material is admixed with a mixture of a dipolar aprotic intercrystalline swelling agent and an ionic liquid. This method results in the complete dissolution of the cellulose and destruction of the fiber morphology of the cellulose. Although the cellulose may be regenerated using a non-solvent, the crystallinity of the regenerated cellulose is lower than the original cellulose sample.

WO 2013/171364 teaches a method of separating hemicellulose and cellulose by dissolution of hemicellulose from a hemicellulose-rich source, such as a pulp of any origin or from holocellulose. In the method, hemicellulose is dissolved in a solvent system comprising a cellulose solvent, which is either a ionic liquid or another direct cellulose solvent, and a molecular solvent (co-solvent), wherein said co-solvent does not dissolve cellulose, and wherein the solvent basicity and acidity of said ionic liquid or other direct cellulose solvent are adequately adjusted by the co-solvent. WO 2013/171364 describes having quantitative separation of cellulose and hemicellulose without any depolymerization and yield losses as occurring during conventional dissolving pulp manufacturing processes.

U.S. Pat. No. 5,865,898 discloses methods for the pretreatment of a lignocelluloses-containing biomass. The pretreatment may include the addition of calcium hydroxide and water to the biomass to form a mixture, and then subjecting the mixture to relatively high temperatures for a period of time sufficient to render the biomass amenable to digestion. Alternatively, the pretreatment process includes the addition of an oxidizing agent, selected from the group consisting of oxygen and oxygen-containing gasses, to the mixture under pressure. U.S. Pat. No. 5,865,898 further discloses physicochemical pretreatments including steam explosion and ammonia fiber explosion, chemical pretreatments, biological pretreatments, and physical pretreatments.

Galletti et al. disclose biomass pre-treatment methods for the separation of cellulose, hemicellulose, and lignin. Examples of the biomass include hardwood stems, softwood stems, rice straw, wheat straw, tobacco chops, arundo donax, miscanthus, and newpaper. Numerous pre-treatment methods are disclosed, including milling, torrefaction, steam explosion, liquid hot water, ammonia fiber explosion, carbon dioxide explosion, alkaline, acid, ozonolysis, organosolv and ionic liquid. Galletti et al., Biomass pre-treatment: separation of cellulose, hemicellulose and lignin. Existing Technologies and perspectives. Eurobioref., Sep. 19, 2011.

The need exists for processes for producing high purity cellulose from lower grade starting materials without destroying the fiber morphology and other characteristics of the cellulose structure. In particular, the need exists for cost effective processes for removing and recovering hemicellulose from cellulosic materials to yield high purity cellulose that can be converted to cellulose derivatives.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a process for purifying a cellulosic material, comprising: pretreating the cellulosic material to form a pretreated cellulosic material; extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the cellulosic material. The cellulosic material may be delignified prior to the pretreatment. The extracting may comprise a single extraction step or multiple extraction steps. The cellulosic material may be a pulp with a water content from 1 wt. % to 50 wt. %. The pretreating may be conducted at a temperature from 90 to 250° C. The pretreating may comprise steam explosion, ammonia fiber explosion, carbon dioxide explosion, alkaline hydrolysis, sodium hydroxide pretreatment, calcium hydroxide pretreatment, or combinations thereof. The pretreating may comprise water pretreating, dilute acid pretreating, or a combination thereof. In some aspects, the pretreating comprises water pretreating conducted at a pulp to water weight ratio from 1:5 to 1:100. The temperature may range from 50 to 250° C. In other aspects, the pretreating comprise may dilute acid pretreating conducted at a pulp to dilute acid solution weight ratio from 1:5 to 1:100. The temperature may range from 20 to 150° C. and the pressure may range from 50 kPa to 10,000 kPa, or from 100 kPa to 5,000 kPa. The acid may be selected from the group consisting of an organic acid selected from the group consisting of formic acid, acetic acid, propionic acid, oxalic acid, and maleic acid; an inorganic acid selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid; and combinations thereof. The acid may be present in an aqueous solution in a concentration from 0.0001 to 10 wt. %. The acid may be dilute sulfuric acid at a pH from 1 to 6. The cellulosic product may have a measured UV value for purity at 277 nm of less than 2, or of less than 1.1. The separating may comprise filtering and washing the extraction mixture. The washing may be conducted with a washing agent selected from the group consisting of methanol, ethanol, isopropanol, acetone, methyl isobutyl ketone, propionitrile, butyronitrile, chloroacetonitrile, ether, tetrahydrofuran, acetone, acetic acid, formic acid, water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, a mixture of water and alcohol, and combinations thereof.

The co-solvent may be selected from the group consisting of alcohols, esters, ethers, ketones, carboxylic acids, nitriles, amines, amides, halides, hydrocarbon compounds, heterocyclic compounds, and combinations thereof. In some aspects, the co-solvent is selected from the group consisting of methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, tetrahydrofuran, acetone, acetic acid, formic acid, acetonitrile, propionitrile, butyronitrile, chloroacetonitrile, dichloromethane, chloroform, triethylamine, N,N-dimethylformamide, toluene, pyridine, water, and combinations thereof.

The cellulose solvent may comprise an ionic liquid selected from the group consisting of ammonium-based ionic substances, imidazolium-based ionic substances, phosphonium-based ionic substances, and combinations thereof. In some aspects, the cellulose solvent comprises an ionic liquid selected from the group consisting of ammonium acetate, hydroxyethyl ammonium acetate, hydroxyethyl ammonium formate, tetramethylammonium acetate, tetrabutylammonium acetate, tetraethylammonium acetate, benzyltriethylammonium acetate, benzyltributylammonium acetate, benzyltriethylammonium chloride, benzyltributylammonium chloride, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, N,N-dimethylpyrrolidinium acetate, N,N-dimethylpiperidinium acetate, N,N-dimethylpyrrolidinium dimethyl phosphate, N,N-dimethylpiperidinium dimethyl phosphate, N,N-dimethylpyrrolidinium chloride, N,N-dimethylpiperidinium chloride, and combinations thereof. In other aspects, the cellulose solvent comprises an ionic liquid selected from the group consisting of 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1-ethyl-3-ethyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate, 1,3-dimethylimidazolium dimethyl phosphate and combinations and complexes thereof. In still further aspects, the cellulose solvent comprises an amine oxide selected from the group consisting of trimethylamine N-oxide, triethylamine N-oxide, tripropylamine N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide, N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide, and combinations thereof. In some aspects, the cellulose solvent comprises an ionic liquid selected from the group consisting of ethyltributylphosphonium diethylphosphate, methyltributylphosphonium dimethylphosphate, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tributylmethylphosphonium methylsulfate, trihexyltetradecylphosphonium decanoate, trihexyltetradecylphosphonium dicyanamide, ethyltriphenylphosphonium acetate, ethyltributylphosphonium acetate, benzyltriethylphosphonium acetate, benzyltributylphosphonium acetate, tetrabutylphosphonium acetate, tetraethylphosphonium acetate, tetramethylphosphonium acetate, and combinations thereof.

In another embodiment, the present invention is directed to a process for purifying a cellulosic material, comprising: subjecting the cellulosic material to a dilute acid pretreatment to form a pretreated cellulosic material; extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the pretreated cellulosic material.

In another embodiment, the present invention is directed to a process for purifying a cellulosic material, comprising: delignifying the cellulosic material to form a wet cellulosic material comprising at least 5 wt. % water; subjecting the wet cellulosic material to a dilute acid pretreatment to form a pretreated cellulosic material; extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the pretreated cellulosic material. The delignifying may comprise combining a starting cellulosic material and a cooking liquor to dissolve lignin to form a cooked cellulosic material comprising cooking liquor, dissolved lignin and cellulosic material; and separating the cooking liquor and lignin from the cellulosic material to form the wet cellulosic material. The process may further comprise complete or partial bleaching or washing of the wet pulp prior to the extracting.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be better understood in view of the appended non-limiting figure, in which:

FIG. 1 shows an exemplary purification process in accordance with one embodiment of the present invention;

FIG. 2 shows an exemplary purification process in accordance with another embodiment of the present invention;

FIG. 3 shows an exemplary purification process in accordance with yet another embodiment of the present invention; and

FIG. 4 shows a pulping process in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION I. Introduction

The present invention relates to processes for purifying a cellulosic material comprising pretreating the cellulosic material to form a pretreated cellulosic material; extracting hemicellulose and other cellulosic impurities (e.g., dichloromethane (DCM) extractables and degraded cellulose) from the pretreated cellulosic material with an extractant to form an extraction mixture; and separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the cellulosic material. The extractant comprises a cellulose solvent and a co-solvent. The cellulose solvent should be suitable for dissolving hemicellulose, and preferably degraded cellulose and other impurities in the cellulosic material, but should have little solubility for α-cellulose. The cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide and combinations thereof, and the cellulose co-solvent is preferably selected from the group consisting of dimethyl sulfoxide (“DMSO”), tetramethylene sulfone, tetramethylene sulfoxide, N-methyl pyrrolidone, dimethyl formamide (“DMF”), acetonitrile, acetic acid, water, and mixtures thereof. As used herein, a “pretreatment” step refers to a step of contacting a cellulosic material with a pretreating agent under conditions effective to form a pretreated cellulosic material that when extracted forms a final cellulosic material having a lower hemicellulose content, e.g., at least 5% lower, at least 10% lower or at least 15% lower hemicellulose content, than a comparable cellulosic material that has been similarly extracted but without a pretreatment step.

The processes of the invention are particularly suitable for separating and removing impurities, such as hemicellulose and/or degraded cellulose, from a cellulosic material to form a finished cellulosic product, the purity of which may vary widely depending largely on the composition of the starting cellulosic material, the composition of the extractant used, and extraction conditions. In preferred aspects, the finished cellulose product comprises dissolvable grade cellulose, such as acetate (or higher) grade cellulose.

By subjecting the cellulosic material to a pretreatment process in combination with one or more extraction steps, the UV purity and final molecular weight of the final cellulosic product may be advantageously controlled, resulting in energy and cost savings. While the composition and components of the cellulosic material, including hemicellulose components, may vary based on the source of the material, xylan is a prominent hemicellulose component of hardwood. UV purity may be used to determine xylan content with a lower UV absorbance indicating a lower xylan content. The procedure for UV absorbance measurement is described further herein but briefly includes twice drying the pulp and recording the weight. The dried pulp is then hydrolyzed with sulfuric acid and diluted with water to convert xylan to furfural while leaving the cellulose unaffected due to the difference of sugar dehydration rates. The UV absorbance from 210 to 600 nm is then measured and the peak values at 277 nm and 600 nm are recorded. The normalization of UV absorbance is carried out using the formula:

${{UV}\mspace{14mu} {absorbance}_{{norm}.}} = \frac{\left( {{Abs}_{277{nm}} - {Abs}_{600{nm}}} \right)}{{Wt}._{{dry}\mspace{14mu} {pulp}}}$

With the combination of a pretreatment step and extraction, a final cellulosic product may be formed having a measured UV value for purity at 277 nm of less than 2, e.g., less than 1.1, less than 1, less than 0.9 or less than 0.8. In terms of ranges, the final cellulosic product may have a measured UV value for purity at 277 nm that ranges from 0.7 to 2, e.g., from 0.7 to 1.1, from 0.7 to 1, from 0.7 to 0.9 or from 0.7 to 0.8. Without being bound by theory, pretreating may advantageously selectively break down high molecular weight hemicellulose components, rendering them more suitable for extraction. In addition to the improved UV purity of the final cellulosic product, pretreating the cellulosic material may also reduce the relatively high molecular weight of the cellulosic material, allowing the final cellulosic product to meet conventional processing conditions for acetate grade pulp. Further, pretreating the cellulosic material may also adjust acetylation performance and the crystallinity the final cellulosic product.

The pretreatment processes for the processes of the invention may comprise one or more of steam explosion, ammonia fiber explosion, carbon dioxide explosion, alkaline hydrolysis, sodium hydroxide pretreatment, calcium hydroxide pretreatment, or a combination thereof. In some embodiments, the pretreatment process may be selected from water pretreating, dilute acid pretreating, and combinations thereof.

II. Cellulosic Material

The present invention is broadly applicable to the treatment of natural cellulosic materials, including plant and plant-derived materials. As used herein, the term “cellulosic material” refers to any material comprising cellulose, such as a pulp, and which may contain, for example, α-cellulose, hemicellulose and degraded cellulose. In preferred embodiments, the cellulosic material comprises wood pulp, e.g., paper grade wood pulp. When the cellulosic material is paper grade wood pulp, the processes described herein may be advantageously used to produce acetate grade wood pulp from the paper grade wood pulp, although the processes of the invention are not limited to the use of paper grade wood pulp as the starting cellulosic material or to the formation of acetate grade wood pulp as the final cellulosic material.

In some embodiments, the cellulosic material may comprise a cellulosic raw material, which may include, without limitation, plant derived biomass, corn stover, sugar cane stalk, bagasse and cane residues, rice and wheat straw, agricultural grasses, hard wood, hardwood pulp, soft wood, softwood pulp, herbs, recycled paper, waste paper, wood chips, pulp and paper wastes, waste wood, thinned wood, cornstalk, chaff, and other forms of wood, bamboo, soyhull, bast fibers, such as kenaf, hemp, jute and flax, agricultural residual products, agricultural wastes, excretions of livestock, microbial, algal cellulose, and all other materials proximately or ultimately derived from plants. Such cellulosic raw materials are preferably processed in pellet, chip, clip, sheet, attritioned fiber, powder form, or other form rendering them suitable for extraction with the extractant.

Generally, cellulosic material may be derived from lignin-containing materials, where lignin has been removed therefrom. In cellulosic materials, hemicellulose is linked to cellulose by hydrogen bonds. Overall, the cellulose material has a linear shape of fiber morphology, which is surrounded by hemicellulose via hydrogen bonds. These bonds may become weakened by treating the cellulosic material with an extractant to selectively dissolve the hemicellulose while maintaining the fiber morphology of the cellulose material, e.g., leaving the fiber morphology unchanged.

In one embodiment of the invention, the cellulosic material is a paper grade pulp provided in forms such as, but not limited to, rolls, sheets, or bales. Preferably, the paper grade pulp comprises at least 70 wt. % α-cellulose, e.g., at least 80 wt. % α-cellulose or at least 85 wt. % α-cellulose. Paper grade pulp typically also comprises at least 5 wt. % hemicellulose, at least 10 wt. % hemicellulose or at least 15 wt. % hemicellulose. In another embodiment, the cellulosic material may be another α-cellulose containing pulp, such as viscose grade pulp, rayon grade pulp, semi-bleached pulp, unbleached pulp, bleach pulp, Kraft pulp, absorbent pulp, dissolving pulp, or fluff. While these cellulosic materials comprise various concentrations of α-cellulose, the inventive processes may be advantageously used to treat them, based on optimized process design, to produce higher purity α-cellulose products, optionally up to or exceeding acetate-grade pulp.

The water content of the cellulosic material may vary depending on the source of the cellulosic material and depending on whether the cellulosic material has been subjected to delignification, washing or drying processes. In some aspects, for example, the cellulosic material comprises from 1 to 50 wt. % water, e.g., from 1 to 30 wt. % or from 1 to 15 wt. %.

Cellulose is a straight chain polymer and is derived from D-glucose units, which condense through β-1,4-glycosidic bonds. This linkage motif contrasts with that for α-1,4-glycosidic bonds present in starch, glycogen, and other carbohydrates. Unlike starch, there is no coiling or branching in cellulose and cellulose adopts an extended and rather stiff rod-like confirmation, which is aided by the equatorial confirmation of the glucose residues. The multiple hydroxyl groups on the glucose from one chain form hydrogen bonds with oxygen atoms on the same or on a neighboring chain, holding the chains firmly together side-by-side and forming microfibrils with high tensile strength, which then overlay to form the macrostructure of a cellulose fiber. In preferred embodiments of the invention, the finished cellulosic product retains its fiber structure throughout and after the extraction step.

As used herein, the term “hemicellulose” refers to any of several heteropolymers, e.g., polysaccharides, present in plant cell walls. Hemicellulose can include any one of xylan, glucuronoxylan, arabinoxylan, glucomannan, galactomannan, and xyloglucan. These polysaccharides contain many different sugar monomers and can be hydrolyzed to invert sugars, such as xylose, mannose, galactose, rhamnose and arabinose. Xylose is typically the primary sugar present in hard woods and mannose is the primary sugar present in softwoods.

The processes of the present invention are particularly beneficial in that they are effective for use with paper grade wood pulp that is derived from softwoods or from hardwoods. The processes of the present invention provide a technique for upgrading paper grade pulp produced from softwood species, which are generally more abundant and faster growing than most hardwood species.

Softwood is a generic term typically used in reference to wood from conifers (i.e., needle-bearing trees from the order Pinales). Softwood-producing trees include pine, spruce, cedar, fir, larch, douglas-fir, hemlock, cypress, redwood and yew. Conversely, the term hardwood is typically used in reference to wood from broad-leaved or angiosperm trees. The terms “softwood” and “hardwood” do not necessarily describe the actual hardness of the wood. While, on average, hardwood is of greater density and hardness than softwood, there is considerable variation in actual wood hardness in both groups, and some softwood trees can actually produce wood that is harder than wood from hardwood trees. One feature separating hardwoods from softwoods is the presence of pores, or vessels, in hardwood trees, which are absent in softwood trees. On a microscopic level, softwood contains two types of cells, longitudinal wood fibers (or tracheids) and transverse ray cells. In softwood, water transport within the tree is via the tracheids rather than the pores of hardwoods.

III. Pretreatment

The cellulosic material, which has preferably been delignified, retains a significant amount of hemicellulose and other impurities which necessitate further purification of the cellulosic material. This further purification may include at least one pretreatment step, i.e., a step after delignification but before extraction as described herein. In a paper mill or a pulping mill, for example, the location of the pretreatment step may be after the pulp digester, but in between, before or after bleaching/washing locations. For example, the pretreatment (and extraction) may be in between two or more bleaching locations or between two or more washing locations. The pretreatment step may be selected based on the amount of hemicellulose and other impurities remaining in the cellulosic material after delignification. By pretreating a pulp, e.g., a paper grade pulp, and then subjecting it to an extraction process, optionally with a single extraction step, it has now been surprisingly and unexpectedly discovered that the UV purity of the cellulosic material may be improved when compared to commercially available dissolvable-grade pulps. Furthermore, the relatively high molecular weight of the pulp is also favorably reduced to meet the conventional processing conditions of acetate grade pulp. Finally, the pretreatment step may potentially adjust the acetylation performance and the crystallinity of the final pulp product.

In the present invention, the pretreatment step comprises contacting the cellulosic material with a pretreating agent. The pretreating agent depends on the type of pretreatment used. The pretreatment may comprise steam explosion, ammonia fiber explosion, carbon dioxide explosion, alkaline hydrolysis, sodium hydroxide pretreatment, calcium hydroxide pretreatment, or a combination of any of these pretreatments. Thus, the pretreating agent may be steam, ammonia, carbon dioxide, and alkaline, sodium hydroxide, and/or calcium hydroxide. In some embodiments, the pretreatment step is selected from the group consisting of water pretreatment and dilute acid pretreatment. In a water pretreatment, the pretreating agent is water. In a dilute acid pretreatment, the pretreating agent is a dilute acid. The dilute acid may be selected from the group consisting of: 1) an organic carboxylic acid such as acetic acid, formic acid, propanoic acid, butanoic acid, oxalic acid, and maleic acid, 2) larger fatty acids such as oleic acid and stearic acid, and 3) an inorganic acid such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid; and 4) combinations of any of the organic, larger fatty acids, and inorganic acids. In some embodiments, the dilute acid may be acetic acid or sulfuric acid. Generally, the pretreatment is conducted at a temperature from 20 to 250° C., e.g., from 50 to 200° C. or from 90 to 150° C., but depending on the specific pretreatment process and cellulosic material components, temperatures outside these ranges may be used.

The steam explosion pretreatment includes both physical and chemical methods to break the structure of the cellulosic material. The process may comprise applying steam at high pressure to heat and pressurize any gases and fluids present inside the cellulosic material to internally explode the bulk structure of the cellulosic material via a rapid depressurization of the cellulosic material with the increased moisture content. U.S. Pat. No. 6,506,282, the entirety of which is incorporated herein by reference, discloses a steam explosion pretreatment to disintegrate or defiberize wood fibers. Generally, the pressure may range from 200 kPa to 5000 kPa and the temperature may range from 130 to 260° C. The treatment may have a relatively short duration, optionally having a residence time from 1 to 10 minutes. The process is typically used to improve the reactivity of the cellulosic material toward other catalytic reactions. Steam explosion may hydrolyze the hemicellulose and dehydrate degraded monosaccharides, which results in lower hemicellulose concentration and associated UV purity. However, steam explosion may generate undesirable derivatives, including furan derivatives, necessitating washing of the cellulosic material to remove these derivatives. In some steam explosion processes, an acid such as sulfuric acid or oxalic acid, may be included in the process to decrease the temperature and residence time of the process. However, these additions may require further treatment of the cellulosic material.

Ammonia fiber explosion (“AFEX”) is similar to steam explosion and is disclosed in U.S. Pub. 2003/0150065, the entirety of which is incorporated herein by reference. In this pretreatment step, liquid ammonia penetrates cellulosic fibers in a pressurized environment to plasticize the cellulosic material. The mixture is then exploded to produce a course fibrous material that may be further separated. The pressure may range from 600 to 2000 kPa. The fibers may be pressurized for 0.5 to 30 minutes and the weight ratio of liquid ammonia to dry cellulosic material may range from 1:1 to 8:1. The amount of ammonia used is determined based on the composition of the cellulosic material. The ammonia may be in the form of acetamide. The ammonia is vaporized and may be recovered and recycled. AFEX allows for almost complete solids recovery with no liquid dissolved fractions. The cellulosic material may have increased digestibility as a result of cellulose decrystallization, cleavage of lignin-carbohydrate linkages, enhanced surface area, and wettability.

An alternative to AFEX is carbon dioxide explosion, which uses carbon dioxide as a supercritical fluid. Carbon dioxide explosion is conducted at a lower temperature than AFEX and may be more economically favorable. Carbon dioxide explosion is known to remove lignin, increase substrate digestability and, with the addition of co-solvents, may further improve the delignification process. The process is non-toxic, non-flammable, environmentally acceptable, and provides for low cost and easy recovery of the cellulosic material.

Another pretreatment step is alkaline hydrolysis, which involves combining the cellulosic material with a hot aqueous alkaline solution and which may be used to degrade simple sugars in the cellulosic material, e.g., glucose, galactose and mannose. The alkaline solution may comprise sodium hydroxide, calcium hydroxide, ammonia, or other strong bases, such as potassium hydroxide. Alkaline hydrolysis degrades the ester and glycosidic side chains, resulting in a structural alteration of lignin, cellulose swelling, partial decrystallization of cellulose, and partial solvation of hemicellulose. Thus, alkaline hydrolysis disrupts the lignin structure, increases internal surface area, and separates the structural linkages between the lignin and the carbohydrates. The process is run at lower temperatures and pressures than steam explosion and AFEX, and may cause less sugar degradation. When calcium hydroxide is used in the alkaline solution, the calcium hydroxide is slurried with water and sprayed onto the cellulosic material at ambient or elevated temperatures from 1 hour to 3 weeks. When ammonia is used in the alkaline solution, the process may comprise ammonia recycle percolation, a high severity, low contact time process, or soaking in aqueous ammonia, a low severity, high contact time process. In some aspects, the alkaline hydrolysis may be combined with a physical process, such as irradiation.

In some embodiments, the pretreatment step is selected from the group consisting of water pretreatment and dilute acid pretreatment. Water pretreatment may be used to dissolve and depolymerize hemicellulose and to further improve the UV purity of the pulp after extraction. When the pretreatment is a water pretreatment, the pulp may be combined with water in a pulp to water weight ratio from 1:5 to 1:100, e.g., from 1:5 to 1:50 or from 1:5 to 1:15. Once combined, the mixture may be heated to a temperature from 50 to 250° C., e.g., from 100 to 250° C. or from 110 to 230° C. The operating pressure may vary from 50 up to 10000 kPa, e.g., from 100 kPa to 5000 kPa. The mixture may be kept at this temperature from 1 minute to 5 hours, e.g., from 10 minutes to 3 hours or from 30 minutes to 1 hour. The pulp may then be collected by filtration, washed with a solvent such as water or acetone, de-liquored, and dried to form a pretreated pulp.

Dilute acid pretreatment may similarly be used to improve UV purity of the pulp. The acid may be selected from the group consisting of formic acid, acetic acid, propionic acid, oxalic acid, maleic acid, sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, and combinations thereof. The acid may be present in an aqueous solution in a concentration from 0.0001 to 10 wt. %, e.g., from 0.01 to 7.5 wt. % or from 0.1 to 5 wt. %.

In some aspects, the acid may be acetic acid or sulfuric acid. When the acid is acetic acid, a dilute acid solution may comprise from 0.1 to 10 wt. % acetic acid, e.g., from 0.5 to 7.5 wt. % acetic acid or from 0.6 to 5 wt. % acetic acid. The dilute acetic acid solution may be prepared by combining glacial acetic acid with water prior to combining with the pulp. When the acid is sulfuric acid, the pH of the dilute acid solution is controlled to be from 1 to 6, e.g., from 1.5 to 4.5 or from 2 to 4. The dilute sulfuric acid solution may be prepared by combined sulfuric acid with water until the desired pH is achieved. For both dilute acetic acid and dilute sulfuric acid pretreatment, the pulp to dilute acid solution weight ratio may range from 1:5 to 1:100, e.g., from 1:10 to 1:80 or from 1:30 to 1:50. Once combined with the dilute acid solution, the pulp may be heated in an autoclave or another type of agitating equipment to a temperature from 20 to 150° C., e.g., from 50 to 140° C. or from 100 to 130° C. The operating pressure may vary from 50 kPa to 10000 kPa, e.g., from 100 kPa to 5000 kPa. The mixture may be kept at this temperature from 10 minutes to 5 hours, e.g., from 30 minutes to 3 hours or from 45 minutes to 90 minutes. The pulp may then be collected by filtration, deliquored, washed with a solvent such as water or acetone, de-liquored again, and dried to form a pretreated pulp. Additional steps may be added depending on requirements for the final product, e.g., water content, solvent content, molecular weight, etc.

IV. Extractant

As described above, hemicellulose and optionally degraded cellulose is extracted from the pretreated cellulosic material, e.g., pretreated pulp, using an extractant. The extractant comprises a cellulose solvent and a co-solvent. The cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide and mixtures thereof, examples of which are described below. The cellulose solvent may or (more preferably) may not fully dissolve α-cellulose, but preferably dissolves at least hemicellulose and degraded cellulose, α-cellulose preferably is less soluble in the co-solvent than in the cellulose solvent.

a. Ionic Liquid

Ionic liquids are organic salts with low melting points, preferably less than 200° C., less than 150° C., or less than 100° C., many of which are consequently liquid at room temperature. Specific features that make ionic liquids suitable for use in the present invention are their general lack of vapor pressure, their ability to dissolve a wide range of organic compounds and the versatility of their chemical and physical properties. In addition, ionic liquids are non-flammable making them particularly suitable for use in industrial applications. In some embodiments, the cellulose solvent comprises one or more ionic liquids.

It has been found that, in addition to these beneficial properties, when contacted with cellulosic materials, including plant matter and plant matter derivatives, the ionic liquids are capable of acting as a cellulose solvent, dissolving the hemicellulose and cellulose contained therein. In addition, with the appropriate choice of treatment conditions (for example, duration of contact, temperature, and co-solvent composition), ionic liquids penetrate the structure of the cellulose-containing material to break down the material and extract organic species therein. In particular when used in combination with one or more co-solvents, α-cellulosic components remaining in the cellulosic material are preserved and the fiber morphology is advantageously retained.

Ionic liquids, in pure form, generally are comprised of ions and do not necessitate a separate solvent for ion formation. Ionic liquids existing in a liquid phase at room temperature are called room temperature ionic liquids. Generally, ionic liquids are formed of large-sized cations and a smaller-sized anion. Cations of ionic liquids may comprise nitrogen, phosphorous, sulfur, or carbon. Because of the disparity in size between the cation and anion, the lattice energy of the compound is decreased resulting in a less crystalline structure with a low melting point.

Exemplary ionic liquids include the compounds expressed by the following Formula (1):

[A]⁺[B]⁻  (1)

In one embodiment, the ionic liquid is selected from the group consisting of substituted or unsubstituted imidazolium salts, pyridinium salts, ammonium salts, triazolium salts, pyrazolium salt, pyrrolidinium salt, piperidium salt, and phosphonium salts. In preferred embodiments, [A]⁺ is selected from the group consisting of:

wherein R₁, R₂, R₃, R₄, R₅, R₆ and R₇ are each independently selected from the group consisting of hydrogen, C₁-C₁₅ alkyls, C₂-C₁₅ aryls, and C₂-C₂₀ alkenes, and the alkyl, aryl or alkene may be substituted by a substituent selected from the group consisting of sulfone, sulfoxide, thioester, ether, amide, hydroxyl and amine. [B]⁻ is preferably selected from the group consisting of Cl⁻, Br⁻, I⁻, OH⁻, NO₃ ⁻, SO₄ ²⁻, CF₃CO₂ ⁻, CF₃SO₃ ⁻, BF₄ ⁻, PF₆ ⁻, CH₃COO⁻, (CF₄SO₂)₂N⁻, AlCl₄ ⁻, HCOO⁻, CH₃SO₄ ⁻, (CH₃)₂PO₄ ⁻, (C₂H₅)₂PO₄ ⁻ and CH₃HPO₄ ⁻.

Examples of ionic liquids include tetrabutylammonium hydroxide 30 hydrate (TBAOH.30H₂O), benzyltriethylammonium acetate (BnTEAAc), tetraethylammonium acetate tetrahydrate (TEAAc.4H₂O), benzyltrimethylammonium hydroxide (BnTMAOH), tetramethylammonium hydroxide (TMAOH), ammonium acetate, hydroxyethylammonium acetate, hydroxyethylammonium formate, tetramethylammonium acetate, tetraethylammonium acetate, tetrabutylammonium acetate, tetrabutylammonium hydroxide, 1-butyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1-ethyl-3-ethyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, and mixtures or complexes thereof, but the disclosed concept of utilizing ionic liquids is not limited to the disclosed species.

In some embodiments, the ionic liquid is selected from the group consisting of ammonium-based ionic substances, imidazolium-based ionic substances, phosphonium-based ionic substances, and mixtures thereof. The ammonium-based ionic liquid may be selected from the group consisting of ammonium acetate, hydroxyethylammonium acetate, hydroxyethylammonium formate, tetramethylammonium acetate, tetrabutylammonium acetate, tetraethylammonium acetate, benzyltriethylammonium acetate, benzyltributyl ammonium acetate and combinations thereof. The imidazolium-based ionic liquid may be selected from the group consisting of 1-butyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1-ethyl-3-ethyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, I-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate (EMIMDEP), 1,3-dimethylimidazolium dimethyl phosphate (DMIMDMP) and mixtures or complexes thereof. The ionic liquid may also be selected from the group consisting of N,N-dimethylpyrrolidinium acetate, N,N-dimethylpiperidinium acetate, N,N-dimethylpyrrolidinium dimethyl phosphate, N,N-dimethylpiperidinium dimethyl phosphate, N,N-dimethylpyrrolidinium chloride, N,N-dimethylpiperidinium chloride, and combinations thereof.

In still other embodiments, the ionic liquid may be selected from the group consisting of 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1,3-diethylimidazolium acetate (EEIM Ac), 1-ethyl-3-methyl imidazolium acetate, 1-ethyl-3-ethyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate, 1,3-dimethylimidazolium dimethyl phosphate and combinations and complexes thereof.

In further embodiments, the ionic liquid may be selected from the group consisting of ethyltributylphosphonium diethylphosphate, methyltributylphosphonium dimethylphosphate, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tributylmethylphosphonium methylsulfate, trihexyltetradecylphosphonium decanoate, trihexyltetradecylphosphonium dicyanamide, ethyltriphenylphosphonium acetate, ethyltributylphosphonium acetate, benzyltriethylphosphonium acetate, benzyltributylphosphonium acetate, tetrabutylphosphonium acetate, tetraethylphosphonium acetate, tetramethylphosphonium acetate, and combinations thereof.

The ionic liquid may be commercially available, and may include Basionic™ AC 01, Basionic™ AC 09, Basionic™ AC 25, Basionic™ AC 28, Basionic™ AC 75, Basionic™ BC 01, Basionic™ BC 02, Basionic™ FS 01, Basionic™ LQ 01, Basionic™ ST 35, Basionic™ ST 62, Basionic™ ST 70, Basionic™ ST 80, Basionic™ VS 01, and Basionic™ VS 02, but the invention is not limited to use of these species.

In additional aspects, the ionic liquid may comprise a cationic moiety selected from the group consisting of:

wherein the residues R₁₋₅ are independently linear or branched alkyl- (typically C1-C6), alkoxy-, or alkoxyalkyl groups, residues containing aryl moieties, or hydrogen. The anions of the ionic liquids may be halides (fluoride, chloride, bromide and iodide), pseudohalides (cyanide, thiocyanide, cyanate), carboxylates (formate, acetate, propionate, butyrate), alkyl sulphite, alkyl sulphate, trifluoromethane sulfonate, phenyl sulfonate, dialkyl phosphate, dialkyl phosphate, dialkyl phosphonites, and dialkyl phosphonates.

In preferred embodiments, the ionic liquid compound, as shown below, may be 1-ethyl-3-methyl imidazolium acetate (EMIMAc) of the structural formula (2), 1-butyl-3-methyl imidazolium acetate (BMIMAc) of the structural formula (3), 1-ethyl-3-methyl imidazolium dimethylphosphate of structural formula (4), 1-ethyl-3-methyl imidazolium formate of the structural formula (5), tetrabutylammonium acetate (TBAAc) of the structural formula (6), 1-allyl-3-methyl imidazolium chloride of the structural formula (7), or 1-n-butyl-3-methyl imidazolium chloride of the structural formula (8):

b. Amine Oxide

Amine oxides are chemical compounds that contain the functional group R₃N⁺—O⁻, which represents an N—O bond with three additional hydrogen and/or hydrocarbon side chains. Amine oxides are also known as tertiary amines, N-oxides, amine-N-oxide and tertiary amine N-oxides. In one embodiment, amine oxides that are stable in water may be used.

In some embodiments, the amine oxide may be selected from the group consisting of compounds with chemical structure of acyclic R₃N⁺—O⁻, compounds with chemical structure of N-heterocyclic compound N-oxide, and combinations thereof. In further embodiments, the amine oxide may be an acyclic amine oxide compound with structure of R₁R₂R₃N⁺—O⁻, wherein R₁, R₂ and R₃ are alkyl or aryl chains, the same or different, with chain length from 1 to 18, e.g. trimethylamine N-oxide, triethylamine N-oxide, tripropylamine, N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide, monomethyldiethylamine, dimethylmonoethylamine, monomethyldipropylamine, N-dimethyl-, N-diethyl- or N-dipropylcyclohexylamine, N-dimethylmethylcyclohexylamine, pyridine, and pyridine N-oxide.

In some embodiments, the amine oxide may be a cyclic amine oxide compound including the structures such as pyridine, pyrrole, piperidine, pyrrolidine and other N-heterocyclic compounds, e.g., N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide. In some embodiments, the amine oxide may be the combination of the above mentioned acyclic and/or cyclic amine oxides.

In specific embodiments, the amine oxide may be selected from the group consisting of trimethylamine N-oxide, triethylamine N-oxide, tripropylamine N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide, N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide, N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide, N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide, N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide, and combinations thereof.

Cellulose is insoluble in most solvents because of its strong and highly structured intermolecular hydrogen bonding network. Without being bound by theory, NMMO is able to break the hydrogen bonding network that keeps cellulose insoluble in most solvents. Therefore, the use of NMMO alone would destroy the fiber morphology of cellulose. It has now been discovered that by using the proper ratio of an amine oxide, such as NMMO, with a co-solvent, α-cellulosic components in the cellulosic material may be beneficially preserved and the fiber morphology retained. NMMO is typically stored in 50 to 70 vol. %, e.g., 60 vol. %, aqueous solution as pure NMMO tends toward oxygen separation. See, e.g., U.S. Pat. No. 4,748,241, the entirety of which is incorporated herein by reference. Further contaminants in commercial NMMO product, e.g., N-methylmorpholine, peroxides, and acid components, tend to degrade the storage stability. In other words, further application of NMMO needs to address all stability concerns. For example, developed stabilizers like propyl gallate may be added.

c. Co-Solvent

As stated above, the extractant also comprises a co-solvent. Co-solvents in the context of this invention include solvents that do not have the ability to readily dissolve α-cellulose. In exemplary embodiments, the co-solvent is selected from the group consisting of water, acetic acid, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, diols and polyols such as ethanediol and propanediol, amino alcohols such as ethanolamine, diethanolamine and triethanolamine, aromatic solvents, e.g., benzene, toluene, ethylbenzene or xylenes, halogenated solvents, e.g., dichloromethane, chloroform, carbon tetrachloride, dichloroethane or chlorobenzene, aliphatic solvents, e.g., pentane, hexane, heptane, octane, ligroin, petroleum ether, cyclohexane and decalin, ethers, e.g., tetrahydrofuran, diethyl ether, methyl tert-butyl ether and diethylene glycol monomethyl ether, ketones such as acetone and methyl ethyl ketone, esters, e.g., ethyl acetate, dimethyl carbonate, dipropyl carbonate, propylene carbonate, amides, e.g., formamide, dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), DMSO, acetonitrile and mixtures thereof. Since the boiling points of co-solvents vary significantly, the efficient purification processes associated with each co-solvent may not be exactly the same.

In one embodiment, a second co-solvent may be used in conjunction with the first co-solvent and the cellulose solvent, e.g., amine oxide or ionic liquid, as described above. In one embodiment, the second co-solvent decreases the viscosity of the extractant. The second co-solvent may have a viscosity, for example, of less than 2.0 mPa·s, e.g., less than 1.8 mPa·s or less than 1.5 mPa·s at 25° C. In some embodiments, the second co-solvent is selected from the group consisting of formamide, DMF, dimethylacetamide, DMSO, N-methylpyrrolidone, propylene carbonate, acetonitrile and mixtures thereof. It is postulated that using a low viscosity second co-solvent in the extractant, the extraction rate is enhanced and a smaller amount of ionic liquid is needed to extract the hemicellulose in the cellulosic material.

Without being bound by theory, the insolubility of the α-cellulose in the co-solvent and the resulting extractant maintains the cellulose fiber morphology, e.g., leaving the fiber morphology unchanged, while the extractant penetrates the cellulosic material, dissolves and extracts the hemicellulose and preferably degraded cellulose from the cellulosic material. Depending on the specific co-solvent used in the extractant, the weight percentage of the cellulose solvent and the co-solvent in the extractant may vary widely.

d. Extractant Compositions

The specific formulation of the extractant employed may vary widely, depending, for example, on the hemicellulose and degraded cellulose content of the pretreated cellulosic material, and the processing scheme employed. In one embodiment, the extractant optionally comprises at least 0.1 wt. % amine oxide, e.g., at least 2 wt. % or at least 4 wt. %. In terms of upper limits, the extractant optionally comprises at most 85 wt. % amine oxide, e.g., at most 75 wt. %, or at most 70 wt. % amine oxide. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 85 wt. % amine oxide, e.g., from 2 wt. % to 75 wt. %, or from 4 wt. % to 70 wt. %. The extractant optionally comprises at least 0.1 wt. % co-solvent, e.g., at least 1 wt. %, or at least 3 wt. % co-solvent. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. %, at most 98 wt. %, or at most 97 wt. % co-solvent. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 99.9 wt. % co-solvent, e.g., from 1 wt. % to 98 wt. %, or from 3 wt. % to 97 wt. % co-solvent.

In one embodiment, the extractant comprises an aqueous co-solvent, e.g., water, and an amine oxide. For example, the extractant optionally comprises at least 40 wt. % amine oxide, e.g., at least 50 wt. % or at least 60 wt. %. In terms of upper limits, the extractant optionally comprises at most 90 wt. % amine oxide, e.g., at most 85 wt. %, or at most 80 wt. % amine oxide. In terms of ranges, the extractant optionally comprises from 40 wt. % to 90 wt. % amine oxide, e.g., from 50 wt. % to 85 wt. %, or from 60 wt. % to 80 wt. % amine oxide. The extractant optionally comprises at least 1 wt. % aqueous co-solvent, e.g., at least 5 wt. %, or at least 10 wt. % aqueous co-solvent. In terms of upper limits, the extractant optionally comprises at most 50 wt. % aqueous co-solvent, at most 40 wt. %, or at most 30 wt. %. In terms of ranges, the extractant optionally comprises from 1 wt. % to 50 wt. % aqueous co-solvent, e.g., from 5 wt. % to 40 wt. %, or from 10 wt. % to 30 wt. %.

In one embodiment, the extractant comprises an organic co-solvent and an amine oxide. In this aspect, the extractant optionally comprises at least 0.1 wt. % amine oxide, e.g., at least 1 wt. % or at least 2 wt. % amine oxide. In terms of upper limits, the extractant optionally comprises at most 85 wt. % amine oxide, e.g., at most 80 wt. %, or at most 70 wt. %. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 85 wt. % amine oxide, e.g., from 1 wt. % to 80 wt. %, or from 2 wt. % to 70 wt. %. In this aspect, the extractant optionally comprises at least 15 wt. % organic co-solvent, e.g., at least 20 wt. %, or at least 30 wt. %. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. % organic co-solvent, at most 98 wt. %, or at most 97 wt. %. In terms of ranges, the extractant optionally comprises from 15 wt. % to 99.9 wt. % organic co-solvent, e.g., from 20 wt. % to 98 wt. %, or from 30 wt. % to 97 wt. %. In one embodiment, the organic co-solvent is DMSO.

In one embodiment, the extractant includes an amine oxide, a first co-solvent and a second co-solvent. In one embodiment, the extractant includes an amine oxide, an aqueous co-solvent, e.g., water, and an organic co-solvent, e.g., DMSO. In this aspect, the amine oxide concentration may range, for example, from 1 wt. % to 85 wt. %, the water concentration may range from 1 wt. % to 35 wt. %, and the organic co-solvent, e.g., DMSO, concentration may range from 1 wt. % to 98 wt. %.

In other embodiments, the cellulose solvent used in the extractant comprises one or more ionic liquids. For example, the extractant optionally comprises at least 0.1 wt. % ionic liquid, e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper limits, the extractant optionally comprises at most 95 wt. % ionic liquid, e.g., at most 90 wt. %, or at most 85 wt. %. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 95 wt. % ionic liquid, e.g., from 1 wt. % to 90 wt. %, or from 2 wt. % to 85 wt. %. The extractant optionally comprises at least 5 wt. % co-solvent, e.g., at least 10 wt. %, at least 15 wt. %, or at least 20 wt. %. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. % co-solvent, e.g., at most 99 wt. %, or at most 98 wt. %. In terms of ranges, the extractant optionally comprises from 5 wt. % to 99.9 wt. % co-solvent, e.g., from 10 wt. % to 99 wt. %, or from 20 wt. % to 98 wt. %.

In one embodiment, the cellulose solvent comprises one or more ionic liquids and the co-solvent comprises an aqueous co-solvent, e.g., water. In this aspect, the extractant preferably comprises at least 50 wt. % ionic liquid, e.g., at least 65 wt. % or at least 80 wt. %. In terms of upper limits, the extractant optionally comprises at most 95 wt. % ionic liquid, e.g., at most 90 wt. %, or at most 85 wt. %. In terms of ranges, the extractant optionally comprises from 50 wt. % to 95 wt. % ionic liquid, e.g., from 65 wt. % to 90 wt. %, or from 70 wt. % to 85 wt. %. The extractant optionally comprises at least 5 wt. % aqueous co-solvent, e.g., at least 10 wt. %, at least 15 wt. %, or at least 20 wt. %. In terms of upper limits, the extractant optionally comprises at most 50 wt. % aqueous co-solvent, e.g., at most 35 wt. %, or at most 20 wt. % aqueous co-solvent. In terms of ranges, the extractant may comprise from 5 wt. % to 50 wt. % aqueous co-solvent, e.g., from 10 wt. % to 35 wt. %, or from 15 wt. % to 20 wt. %.

In one embodiment, when the extractant comprises one or more ionic liquids as cellulose solvent and an organic co-solvent, the extractant preferably comprises at least 0.1 wt. % ionic liquid, e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper limits, the extractant optionally comprises at most 20 wt. % ionic liquid, e.g., at most 15 wt. %, or at most 10 wt. %. In terms of ranges, the extractant may comprise from 0.1 wt. % to 20 wt. % ionic liquid, e.g., from 1 wt. % to 15 wt. %, or from 2 wt. % to 10 wt. %. The extractant optionally comprises at least 80 wt. % organic co-solvent, e.g., at least 85 wt. %, or at least 90 wt. %. In terms of upper limits, the extractant may comprise at most 99.9 wt. % organic co-solvent, e.g., at most 98 wt. %, or at most 97 wt. %. In terms of ranges, the extractant optionally comprises from 80 wt. % to 99.9 wt. % organic co-solvent, e.g., from 85 wt. % to 98 wt. %, or from 90 wt. % to 97 wt. %. In one embodiment, the organic co-solvent is DMSO.

In one embodiment, when the extractant comprises one or more ionic liquids as cellulose solvent and an organic co-solvent, the extractant preferably comprises at least 0.1 wt. % ionic liquid, e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper limits, the extractant optionally comprises at most 40 wt. % ionic liquid, e.g., at most 30 wt. %, or at most 20 wt. %. In terms of ranges, the extractant may comprise from 0.1 wt. % to 40 wt. % ionic liquid, e.g., from 1 wt. % to 30 wt. %, or from 2 wt. % to 20 wt. %. The extractant optionally comprises at least 60 wt. % organic co-solvent, e.g., at least 70 wt. %, or at least 80 wt. %. In terms of upper limits, the extractant may comprise at most 99.9 wt. % organic co-solvent, e.g., at most 98 wt. %, or at most 97 wt. %. In terms of ranges, the extractant optionally comprises from 60 wt. % to 99.9 wt. % organic co-solvent, e.g., from 70 wt. % to 98 wt. %, or from 80 wt. % to 97 wt. %. In one embodiment, the organic co-solvent is DMSO.

In one embodiment, the extractant includes a cellulose solvent, e.g., amine oxide or ionic liquid, a first co-solvent and a second co-solvent. In this aspect, the weight ratio of first co-solvent to second co-solvent is preferably from 20:1 to 1:20, e.g. from 15:1 to 1:15 or from 10:1 to 1:10. Since the production costs of ionic liquids are generally higher than those of co-solvents, the use of a large amount of the second co-solvent beneficially reduces the cost of purifying the cellulosic material.

In one embodiment, the extractant includes an ionic liquid, a first co-solvent and a second co-solvent. In one embodiment, the extractant includes an ionic liquid, an aqueous co-solvent, e.g., water, and an organic co-solvent, e.g., DMSO. In the tertiary extractant system, the extractant may include at most 50 wt. % ionic liquid, e.g., at most 40 wt. %, or at most 30 wt. %. In terms of lower limit, the extractant may include at least 0.1 wt. % ionic liquid, e.g., at least 5 wt. % or at least 10 wt. %. In terms of ranges, the extractant may include from 0.1 wt. % to 50 wt. % ionic liquid, e.g., from 5 wt. % to 40 wt. %, or from 10 wt. % to 30 wt. %. In some embodiments, the extractant may include at most 20 wt. % the first co-solvent, e.g., at most 16 wt. %, or 10 wt. %. In terms of ranges the extractant may include from 0.5 wt. % to 20 wt. % the first co-solvent, e.g., from 3 wt. % to 16 wt. % or from 5 wt. % to 10 wt. %. In one embodiment, water is the first co-solvent. In one embodiment, DMSO is the second co-solvent. Without being bound by theory, it is postulated that the decrease in viscosity in the extractant by using the second co-solvent beneficially enhances the extraction rate and increases the amount of hemicellulose extracted from the cellulosic material.

In one embodiment, the extractant comprises an aqueous co-solvent, an ionic liquid and an amine oxide. In this aspect, the co-solvent concentration may range, for example, from 5 wt. % to 50 wt. %, the ionic liquid concentration may range from 0.1 wt. % to 50 wt. %, and the amine oxide concentration may range from 0.1 wt. % to 85 wt. %.

In one embodiment, the extractant comprises an organic co-solvent, an ionic liquid and an amine oxide. In this aspect, the co-solvent concentration may, for example, range from 5 wt. % to 99 wt. %, the ionic liquid concentration may range from 0.1 wt. % to 50 wt. %, and the amine oxide concentration may range from 0.1 wt. % to 50 wt. %.

V. Cellulosic Material Purification

As described herein, a cellulosic material, e.g., a delignified pulp, is pretreated prior to extraction. As shown in FIG. 1, process 100 comprises a pretreatment zone 10, a cellulosic purification zone 101, and a hemicellulose purification zone 102. A cellulosic material 11 is fed to pretreatment unit 12 to form a pretreated cellulosic material 103. Pretreatment unit 12 is selected depending on the composition of cellulosic material 11 and on the pretreatment process to be used. For example, when the pretreatment process is steam explosion, AFEX, or carbon dioxide pretreatment, pretreatment unit 12 may comprise a pressurized continuous stirred tank reactor, a tubular reactor suitable for the operations of liquid, gas, and solid phase pretreatment, or a pulp digester. When the pretreatment process is water pretreatment or dilute acid pretreatment, pretreatment unit 12 may comprise an autoclave or other equipment suitable for liquid and solid phase pretreatment. Pretreatment unit 12 may also comprise a filter, washer, filter/washer, and/or drier, again depending on the pretreatment process used. The equipment may be operated horizontally or vertically.

Pretreated cellulosic material 103 is then fed to extractor 105. Line 103 may represent, for example, a slurry pump. However, for a pretreated cellulosic material with reduced water content, other transport apparatus, such as a screw feeder, a belt feeder, a rotary valve feeder, or another type of solid transport equipment, may be applicable. The pretreated cellulosic material may also be subject to a deliquoring operation and/or a pre-extraction wash in order to optimize the water content in the extraction process. Fresh or recycled extractant, comprising a cellulose solvent and co-solvent, as described above, is fed to extractor 105 via line 104. Although pretreated cellulosic material 103 and extractant 104 are shown as fed separately to extractor 105, it is contemplated that they may be completely or partially mixed prior to being fed to extractor 105. Pretreated cellulosic material 103 and extractant 104 may be combined in extractor 105 to form an extraction mixture. In some embodiments, the mass flow ratio of extractant 104 to pretreated cellulosic material 103 may range from 5:1 to 20:1. The extraction mixture within extractor 105 may comprise, for example, from 0.1 to 20 wt. % solids, e.g., from 0.5 to 15 wt. % or from 1.25 to 10 wt. % solids. Accordingly, the water content may be up to 99.9 wt %.

Extractant 104 for extracting hemicellulose and degraded cellulose from pretreated cellulosic material 103 may be any extractant capable of dissolving preferably at least 50% of the hemicellulose, more preferably at least 75% or at least 90% of the hemicellulose, in pretreated cellulosic material 103, as determined by UV absorbance analysis of hemicellulose concentration and mass measurements of the feed, cellulosic product, and hemicellulose product. Extractant 104 comprises a cellulose solvent and co-solvent in relative amounts that do not overly degrade the cellulose. For example, in one embodiment, the extractant dissolves less than 15% of the α-cellulose in pretreated cellulosic material 103, e.g., less than 10%, or less than 5%, as determined similarly by UV absorbance analysis and mass measurements. In some embodiments, the extractant may also dissolve at least 5% lignin, e.g., at least 10%, at least 15%, or at least 20%. As described above, amine oxides and ionic liquids may tend to dissolve α-cellulose. The extractant preferably comprises sufficient co-solvent to reduce α-cellulose solubility in the overall extractant to a point that the α-cellulose does not readily dissolve therein. Preferably, the α-cellulose is substantially insoluble in the co-solvent. Extractant 104 in accordance with the present invention, therefore, has the property of selectively dissolving the hemicellulose, lignin, and preferably degraded cellulose that is in pretreated cellulosic material 103.

Exemplary compositions for the pretreated cellulosic material pulp and extractant fed to the extractor, and for the resulting extraction mixture are provided in Table 1.

TABLE 1 EXTRACTOR 105 Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Pretreated Cellulosic Material 103 Cellulose* 0.1 to 90   5 to 85 10 to 80 Hemicellulose 0.1 to 40  0.1 to 30   1 to 25 Water   1 to 99.9 2.5 to 95   5 to 90 Extractant 104 Solvent  0.1 to 99.9  2 to 90  3 to 80 Co-solvent  0.1 to 99.9 10 to 98 20 to 97 Extraction Mixture in Extractor 105 Cellulose 0.2 to 1.4 0.3 to 13  0.3 to 12  Hemicellulose & 0.008 to 7    0.03 to 5   0.05 to 4   Degraded Cellulose Water 0.001 to 20   0.01 to 16   0.01 to 10   Solvent 0.09 to 99.4 1.7 to 90  2.6 to 80  Co-solvent 0.09 to 99.4 8.5 to 98  17 o 97 *“Cellulose” in this row refers to cellulose of all forms including degraded cellulose

The treatment of pretreated cellulosic material 103 with extractant 104 may be conducted at an elevated temperature, and preferably occurs at atmospheric pressure or slightly above atmospheric pressure. Preferably, the contacting is conducted at a temperature from 20° C. to 300° C., e.g., from 20° C. to 150° C., from 40° C. to 140° C., or from 50° C. to 130° C. In terms of upper limits, the treatment of pretreated cellulosic material 103 may be conducted at a temperature of less than 300° C., e.g., less than 200° C., less than 150° C., less than 140° C. or less than 130° C. In terms of lower limit, the treatment of pretreated cellulosic material 103 may be conducted at a temperature of greater than 20° C., e.g., greater than 40° C., or greater than 80° C. The pressure (absolute, unless otherwise indicated) is in the range from 20 kPa to 20 MPa, preferably from 40 kPa to 10 MPa, more preferably from 100 kPa to 5000 kPa. In some embodiments, the pressure may be optimized, e.g., reduced below 20 kPa in order to maintain a liquid phase for the extraction process.

Pretreated cellulosic material 103 may contact extractant 104 (or have a residence time in extractor 105 for continuous processes) between 5 minutes to 1000 minutes, e.g., between 20 minutes to 500 minutes, or from 40 minutes to 200 minutes. In terms of lower limits, the treatment of pretreated cellulosic material 103 may be for at least 5 minutes, e.g., at least 20 minutes or at least 40 minutes. In terms of upper limits, the treatment of pretreated cellulosic material 103 may be for at most 1000 minutes, e.g., at most 500 minutes, or at most 200 minutes.

The extraction process may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. In a continuous process, pretreated cellulosic material 103 contacts extractant 104 in one or more extraction vessels. In one embodiment, extractant 104 may be heated to the desired temperature before contacting pretreated cellulosic material 103. In one embodiment, the extraction vessel(s) may be heated by any suitable means to the desired temperature. Additionally, an inert gas (not shown), e.g., nitrogen or CO₂, may be supplied to the extractor to improve turbulence in the extractor and improve heat and mass transfer. The flow rate of inert gas will be controlled not to cause hydrodynamic problem, e.g., flooding. When the size and concentration of solid materials along with the flow rate of inert gas are well controlled, the addition of an inert gas may cause the solids in extractor 105 to float on the surface of the extraction mixture allowing for the solids to be skimmed off the surface of the liquid phase contained in extractor 105.

In the extraction step, the mass ratio of extractant to pretreated cellulosic material may range from 5:1 to 500:1, e.g., from 7:1 to 300:1, or from 10:1 to 100:1. The solid:liquid mass ratio may range from 0.005:1 to 0.17:1, e.g., from 0.01:1 to 0.15:1 or from 0.02:1 to 0.1:1, depending on the extraction apparatus and set-up. In one embodiment, a solid:liquid ratio of from 0.01:1 to 0.02:1 or about 0.0125:1 may be used to facilitate the filtration operation in a batch process. In another embodiment, a solid:liquid ratio of 0.1:1 to 0.17:1 can be used, in particular for extractors employing countercurrent extraction. The amount of extractant employed has a significant impact on process economics. Counter-current extraction may achieve greater extraction efficiency while maintaining reasonable extractant usage. Counter-current extraction of solubles from pulp can be accomplished in a variety of commercial equipment such as, but not limited to, a series of agitated tanks or columns with or without baffles, hydrapulpers, continuous belt extractors, and screw extractors. Twin-screw extractors are generally more efficient than single-screw extractors. After extraction, the separation of solid and liquid phases can be completed in suitable commercial equipment, which includes filters, centrifuges, and the like.

In one embodiment, the pretreated cellulosic material is subjected to repeated extraction steps. For example, the pretreated cellulosic material may be treated with the extractant in an initial extraction step followed by one or more additional extraction steps, in the same or multiple extractors, to further extract residual hemicellulose and/or degraded cellulose. In one embodiment, the pretreated cellulosic material may be subjected to an initial extraction step, followed by an extractant wash step (discussed below), followed by a second extraction step. In some embodiments, the pretreated cellulosic material may be subjected to a third or fourth extraction step. When multiple extraction steps are employed, the extractant in each extraction step may be the same or varied to account for the different concentrations of hemicellulose and degraded cellulose in intermediate cellulosic materials between extraction steps. For example, a first extraction step may use an extractant comprising an ionic liquid and a co-solvent and a second extraction step may use an extractant comprising an amine oxide and a co-solvent, or vice versa, optionally with one or more extractant wash steps between and/or after the second extraction step. Similar configurations can be designed and optimized based upon the general chemical engineering principles and process design theory. However, in some preferred embodiments, only one extraction step is used, e.g. a single extraction.

In another embodiment (not shown), the process may further include enzymatic digestion of hemicellulose, extraction and/or isolation of digested hemicellulose and recovery of a cellulosic product with reduced hemicellulose content. Without being bound by theory, by treating the pretreated cellulosic material first with the extractant, enzymes may be better able to penetrate the resulting cellulosic material to hydrolyze residual hemicellulose and/or degraded cellulose contained therein. On the contrary, experimental data has shown that less hemicellulose may be removed from the pretreated cellulosic material if it is first treated with an enzyme cocktail under optimum enzyme hydrolysis conditions, followed by an extraction step. For enzymes to be effective in hydrolyzing hemicellulose, the water in the pretreated cellulosic material may improve the pretreatment (e.g., prehydrolysis) of the pulp, which may be utilized to improve the efficiency of the enzymatic hydrolysis of the pulp. The pretreatment step preferably comprises treating the pretreated cellulosic material with high pressure steam, optionally at low or high acid concentrations, or ammonia treatment. Some modification to the process flow scheme may be desired since the enzyme treatment would likely necessitate increased residence time to complete enzymatic hydrolysis. In addition, acidity (pH), temperature and ionic strength would likely need to be adjusted for effective enzymatic treatment.

In this embodiment, after the extraction step, the resulting cellulosic material may be treated with an enzyme, preferably a hemicellulase, to break down residual hemicellulose contained in the cellulosic material. The hemicellulase includes one or more enzymes that hydrolyze hemicellulose to form simpler sugars, ultimately yielding monosaccharides, such as glucose, hexoses and pentoses. Suitable hemicellulase include one or more of xyloglucanase, β-xylosidase, endoxylanase, α-L-arabinofuranosidase, α-glucuronidase, mannanase, and acetyl xylan esterase. Preferably, the enzymes include a combination of both endo-enzymes (i.e., enzymes hydrolyzing internal polysaccharide bonds to form smaller poly- and oligosaccharides) and exo-enzymes (i.e., enzymes hydrolyzing terminal and/or near-terminal polysaccharide bonds) to facilitate the rapid hydrolysis of large polysaccharide molecules. Suitable commercial hemicellulase include SHEARZYME (available from Novozymes A/S, Bagsvaerd, Denmark), PULPZYME (available from Novozymes A/S, Bagsvaerd, Denmark), FRIMASE B210 (available from Puratos, Groot-Bijgaarden, Belgium), FRIMASE B218 (available from Puratos, Groot-Bijgaarden, Belgium), GRINDAMYL (available from Danisco, Copenhagen, Denmark), ECOPULP TX200A (available from AB Enzymes, Darmstadt, Germany), MULTIFECT Xylanase (available from Genencor/Danisco, Palo Alto, USA), PENTOPAN Mono BG (available from Novozymes, Bagsvaerd, Denmark), and PENTOPAN 500 BG (available from Novozymes, Bagsvaerd, Denmark).

The enzymes generally can be used in amounts that are not particularly limited. For example, hemicellulase can be used in amounts ranging from about 0.001 mg/g to about 500 mg/g (e.g., about 0.05 mg/g to about 200 mg/g, about 0.1 mg/g to about 100 mg/g, about 0.2 mg/g to about 50 mg/g, or about 0.3 mg/g to about 40 mg/g). The concentration units are milligrams of enzyme per gram of cellulosic material (e.g., pretreated cellulosic material) to be treated.

After the desired contacting time, an extraction mixture is removed from extractor 105 via line 106. The extraction mixture 106 comprises extractant, dissolved hemicellulose, dissolved degraded cellulose, side products, e.g., mono-, di-, and oligo-saccharide, and an intermediate cellulosic material having reduced hemicellulose content and preferably reduced degraded cellulose content relative to the pretreated cellulosic material composition. Extraction mixture 106 is fed to filter/washer 15 to remove extractant, dissolved hemicellulose, and dissolved degraded cellulose. Removal of the extractant in the filtering step reduces the amount of residual hemicellulose that must be further processed with the intermediate cellulosic material. It also reduces the amount of extractant that must be separated from the intermediate cellulose in subsequent steps. Filter/washer 15 may comprise solid-liquid separation equipment, including but not limited to, for example, rotary vacuum drums, belt filters and screw presses. Filter/washer 15 forms a filtered intermediate cellulosic material 16 and an extraction filtrate 17. Filtered intermediate cellulosic material 16 may be further purified in cellulose purification process system 20 to produce final cellulosic product 22. Extraction filtrate 17 may be further purified in hemicellulose purification process system 30 to produce hemicellulose product 32.

Further exemplary details of cellulosic purification process system 20 and hemicellulose purification process system 30 are shown in FIGS. 2 and 3. As shown in FIG. 2, prior to exiting filter/washer 110, optionally while on a vacuum belt filter, the intermediate cellulosic material may be washed with extractant wash 107 to further reduce the amount of extractant remaining in the filtered extraction mixture. The washing may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. In some embodiments, the intermediate cellulosic material may be washed more than once in separate washing units from filter/washer 110. When more than one washing step is used, the composition of the extractant wash may vary in the different washing steps. For example, a first washing step may use DMSO as an extractant wash to remove residual hemicellulose and a second washing step may use water as an extractant wash to remove residual DMSO. A similar configuration can be designed and optimized based upon the general chemical engineering principles and process design theory.

Extractant wash 107 preferably comprises a co-solvent, which dissolves residual hemicellulose and/or degraded cellulose from the cellulosic material, but may also include some low level of extractant resulting from the sequence of washing steps. In one embodiment, the extractant wash is selected from the group consisting of water, acetonitrile, DMF, DMAC, ketones (e.g. acetone), aldehydes, esters (e.g. methyl acetate, ethyl acetate), ethers (e.g., MTBE), lactones, carboxylic acids (e.g., acetic acid), alcohols, polyols, amino alcohols, DMSO, formamide, propylene carbonate, aromatic solvents, halogenated solvents, aliphatic solvents, vinyl acetate, nitriles (propionitrile, chloroacetonitrile, butyonitrile), chloroform, dichloromethane, and mixtures thereof. In another embodiment, extractant wash 107 is selected from the group consisting of DMSO, DMF, N-methyl pyrrolidone, methanol, ethanol, isopropanol, dimethyl carbonate, propylene carbonate, acetone, water, and mixtures thereof. In some embodiments, at least two extractant washes are used in series, such as DMSO and water. It should be understood that depending on the amount of residual hemicellulose contained in the intermediate cellulosic material, the amount of extractant wash may be minimized to reduce capital cost and energy requirements for subsequent separation and recycle, described below. Additionally, it should be understood that the one or more extractant washes may also be used to remove side products, e.g., mono-, di-, and oligo-saccharides from the extraction mixture.

The extractant wash may further comprise one or more washing aids that improve the removal of extractant from the cellulosic material, improve operability, or otherwise improve the physical properties of the intermediate cellulose material. The washing aids may include, for example, defoamers, surfactants, and mixtures therefore. The amount of washing agent can vary widely based upon the amount of residual extractant, quality requirement for cellulosic product, and process operability.

The extractant wash may then be removed via line 112, e.g., as used extractant wash filtrate. The washed intermediate cellulosic material exits filter/washer 110 as an intermediate cellulosic material 113 having reduced hemicellulose content and preferably reduced degraded cellulose content. Intermediate cellulosic material 113 may comprise less than 6 wt. % extractant, e.g., less than 5 wt. % or less than 4 wt. % extractant. In some embodiments, the intermediate cellulosic material 113 may comprise less than 0.5 wt. % cellulose solvent (ionic liquid and/or amine oxide), e.g., less than 0.05 wt. %, less than 0.005 wt. %, or less than 0.001 wt %. Intermediate cellulosic material 113 may comprise from 9.9 to 99% solids, e.g., from 19 to 90% or from 28 to 85%.

Exemplary compositions using DMSO as the co-solvent and water as the extractant wash for the intermediate cellulosic material are provided in Table 2. When DMSO is used as the co-solvent and water is used as the extractant wash, at least 90% of the cellulose in pretreated cellulosic material 103 is maintained in cellulose product 123, as described herein.

TABLE 2 FILTER/WASHER 110 Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Extraction Mixture 106 Cellulose 0.24 to 14   0.26 to 13   0.29 to 1.2  Hemicellulose & 0.008 to 7    0.03 to 5   0.05 to 5   Degraded Cellulose Solvent (e.g., Ionic 0.09 to 99.4 1.7 to 90  2.6 to 80  Liquid or Amine Oxide) Co-solvent (e.g., DMSO) 0.09 to 99.4 8.5 to 98  17 to 97 Washed Intermediate Cellulosic Material 113 Cellulose 9.9 to 99  19 to 90 28 to 85 Hemicellulose & 0.003 to 12   0.02 to 9   0.06 to 7   Degraded Cellulose Extractant wash  1 to 90 10 to 80 15 to 70 (e.g., water) Extraction Filtrate 111 Cellulose 0.002 to 1.4  0.003 to 1.3  0.003 to 1.2  Hemicellulose & 0.008 to 6.7  0.03 to 5.2  0.05 to 4.4  Degraded Cellulose Solvent (e.g., Ionic 0.09 to 99.9 1.7 to 90  2.6 to 80  Liquid or Amine Oxide) Co-solvent (e.g., DMSO) 0.09 to 99.9  8.5 to 99.6 17.0 to 99.3 Used Extractant wash (Filtrate) 112 Water   91 to 99.8   93 to 99.7   94 to 99.7 Solvent (e.g., Ionic 0.004 to 2.7  0.004 to 2.0  0.004 to 1.5  Liquid or Amine Oxide) Co-solvent (e.g., DMSO) 0.01 to 2.7  0.02 to 2.2  0.03 o 1.9

Intermediate cellulosic material 113 may then be further de-liquored, e.g., mechanically concentrated in a concentrator 115 to form a concentrated cellulosic material 117 having an increased solids content and a residual extractant wash 116, which may be recycled to and combined with either extractant wash 107 or stream 112. The solids content in concentrated cellulosic material 117 may range from 10 to 99 wt %, e.g., from 20 to 90 wt % or from 30 to 85 wt %/o. The concentrator may include squeeze rolls, rotating rolls, and/or ringer rolls as well as optional heat exchangers to vaporize the liquids. Additional water removal methods may be used to concentrate the cellulosic material, depending on the desired solids content and available energy supply. The concentrated cellulosic material may comprise from 2 to 99 wt. % cellulose (e.g., from 3 to 95 wt. % cellulose), from 1 to 60 wt. % water (e.g., from 1 to 50 wt. % water), and from 0.01 to 20 wt. % hemicellulose (e.g., from 0.5 to 10 wt. % hemicellulose).

In some embodiments, when the process comprises more than one washing step, a concentrator may be utilized between washing steps or after all washing steps in order to maximize the washing separation of hemicellulose, as well as improve washing efficiency for the solvent and co-solvent thereby reducing total washing agent quantity required and associated energy and disposal costs.

Concentrated cellulosic material 117 or 113 may then be further dried in dryer 120. Hot gas may be fed to dryer 120 via line 121 and may exit dryer 120 via line 122. A finished cellulose product may then exit dryer 120 via line 123. The dryer may function to remove residual extractant wash. The finished cellulose product may comprise from 80 to 99.9 wt. % cellulose (e.g., from 90 to 95 wt. % cellulose), from 0.01 to 25 wt. % hemicellulose (e.g., from 0.1 to 15 wt. % hemicellulose) and from 0.1 to 20 wt. % water (e.g., from 3 to 15 wt. % water). Exemplary dryers include disintegrator dryers, flash dryers, apron dryers, rotary dryers, heated rolls, infrared dryers, ovens and vacuums. Without being bound by theory, the disintegrator dryer may be used to further open the cellulosic material, which may be advantageous for subsequent processing, e.g., in the formation of cellulose acetate, and derivatives thereof. In another embodiment, dryer 120 comprises heated rolls which may be used to form baled sheets or product rolls of cellulosic material. In some embodiments, the drying unit 50 from the pulping process may be used instead of dryer 120, thus allowing for integration of pulping process and purification process equipment. Finished cellulose product 123 may comprise less than 20 wt. % water, e.g., less than 15 wt. %, less than 10 wt. % or less than 5 wt. % water.

Depending on the purity of the starting material and of the pretreated cellulosic material formed in the pulping process, in accordance to preferred embodiments of the present invention, high purity α-cellulose product may be produced. In preferred embodiments, the finished cellulose product comprises high purity α-cellulose products such as high purity dissolving grade pulps with less than 5 wt. % hemicellulose, e.g., less than 2 wt. % hemicellulose or less than 1 wt. % hemicellulose. In one embodiment, the cellulosic product has a UV absorbance of less than 2.0 at 277 nm, e.g., less than 1.6 at 277 nm, or less than 1.2 at 277 nm. Paper grade pulp typically has a UV absorbance of greater than 4.7 at 277 nm, as determined by standard UV absorbance measurements. Conveniently and accurately, purity of the α-cellulose product may be indicated by a lower absorbance at a certain wavelength.

In addition to retaining the fiber morphology of the cellulosic product, the high purity α-cellulose pulp product also may advantageously retain other beneficial characteristics such as intrinsic viscosity and brightness. The high purity α-cellulose pulp product may be further processed to make cellulose derivatives, such as cellulose ether, cellulose esters, cellulose nitrate, other derivatives of cellulose, or regenerated cellulose fiber, such as viscose, lyocell, rayon, etc. Preferably, the high purity α-cellulose pulp may be used to make cellulose acetate, e.g., cellulose acetate flake or tow.

Returning to extractant filtrate 111, in one embodiment, the stream may be sent to a hemicellulose concentrator 130 to form a (first) recovered extractant 131 and hemicellulose concentrate 132. The recovered extractant 131 will likely be enriched in co-solvent and lean in ionic liquid or amine oxide relative to extractant 104. The hemicellulose concentrator 130 may comprise a filtration unit or an evaporator. The filtration unit may be an ultrafiltration unit or a nanofiltration unit, or membrane separation unit, and may comprise a membrane. The filtration unit may be operated at a pressure from 1 kPa to 5,000 kPa and a temperature from 0° C. to 200° C. and appropriate flow rates. If an evaporator is used, the conditions employed preferably include a pressure from 1 kPa to 1,000 kPa and temperature from 30° C. to 200° C.

Exemplary compositions for the recovered extractant and the hemicellulose concentrate are provided in Table 3.

TABLE 3 Hemicellulose Concentrator 130 Conc. (wt. %) Conc. (wt. %) Conc. (wt %) (First) Recovered Extractant 131 Solvent (e.g., Ionic 0 to 5 0 to 3 0 to 1 Liquid or Amine Oxide) Co-solvent (e.g., DMSO)  95 to 100  97 to 100  99 to 100 Hemicellulose Concentrate 132 Cellulose 0.003 to 0.003 to12.6  0.003 to 11.9  13.4 Hemicellulose &  0.008 to 0.03 to 51   0.06 to 44   Degraded Cellulose 67 Solvent (e.g., Ionic 0.09 to 99.9 1.8 to 99  2.7 to 98  Liquid or Amine Oxide) Co-solvent (e.g., DMSO) 0.009 to 99.3  0.17 to 96   0.26 to 9.3  Water 0.0005 to 0.005 to 2.5  0.005 to 1.8  3.0

The recovered extractant 131 may be recycled to the extractor. In some embodiments, recovered extractant 131 may be combined with extractant 104, as shown. In other embodiments, when recovered extractant 131 consists essentially of co-solvent, recovered extractant 131 may be directly fed to filter/washer 110, or optionally used as a first stage washing agent or combined with extractant wash 107 in washing the intermediate cellulose material.

Hemicellulose concentrate 132 may then be fed to precipitator 135 to precipitate hemicellulose therefrom. Precipitation agent may be fed to precipitator 135 via line 133 and combined with hemicellulose concentrate 132 to form a precipitation slurry 136. Precipitator 135 may comprise one or more stirred tanks or other agitation equipment, and may be either batch or continuous. It may utilize electrostatic charge to facilitate precipitation. Precipitation agent 133 may be selected from the group consisting of an alcohol, e.g., methanol, ethanol, isopropanol, and butanol; ketone, e.g., acetone, 2-butanone; ninitrile, e.g., acetonitrile, propionitrile, butyronitrile, chloroacetonitrile; ether, e.g., tetrahydrofuran, diethyl ether, dibutyl ether; ester, e.g., methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, propylene carbonate; carboxylic acid, e.g., acetic acid, formic acid; amide, e.g., formamide; halide, e.g., dichloromethane, chloroform, 1-chlorobutane, 1,2-dichlorethane; hydrogencarbon compound; e.g., hexane, 2,2,4-trimethylpentane, benzene, toluene; amine, e.g., ethylamine, butylamine, ethyldiamine; heterocyclic compound, e.g., pyridine, pyrrole, pyrrolidine, piperidine; water, and combinations thereof. Precipitation agent 133 may also comprise a mixture of an alcohol and water, optionally at an alcohol:water mass ratio from 0.9:1 to 20:1 from 1:1 to 20:1 or from 2:1 to 15:1. Precipitation slurry 136 may comprise, for example, from 0.001 to 7 wt. % cellulose, from 0.003 to 34 wt. % hemicellulose, from 0.0003 to 7 wt. % water, from 0.05 to 50 wt. % solvent, and from 50 to 99 wt. % precipitation agent.

In another embodiment, a gas, optionally an inert gas, e.g., nitrogen, may be fed to precipitator 135. In some embodiments, the inert gas is carbon dioxide, optionally supercritical carbon dioxide. In this embodiment, the supercritical carbon dioxide may lead to the formation of a carbon dioxide phase, a solvent phase and a hemicellulose phase. In this aspect, hemicellulose is automatically separated out as a solids rich stream. The carbon dioxide may be flashed under low pressure, recovered using a compressor, and returned to precipitator 135. Some or all of the co-solvent may be flashed at reduced pressure and recycled (not shown). This type of concentrating process for hemicellulose may advantageously reduce the downstream washing requirements and associated energy costs (described below).

As shown, precipitation slurry 136 may then be sent to filter/washer 137 which separates a precipitation agent filtrate 139 from recovered solid hemicellulose. Filter/washer 137 may comprise solid-liquid separation equipment, including but not limited to rotary vacuum drums, belt filters and screw presses. Prior to exiting filter/washer 137, the recovered solid hemicellulose may be washed with precipitant wash 134 to form washed recovered solid hemicellulose 138. The washing step may serve to further reduce the amount of extractant and/or precipitation agent remaining in the recovered solid hemicellulose. The washing may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another.

In another embodiment, the precipitator may comprise a crystallizer as long as the hemicellulose solubility is sensitive to solvent temperature. In this aspect, the reduced temperature may cause the hemicellulose to precipitate as solids from the solution.

Precipitant wash 134 preferably comprises a co-solvent, which dissolves the impurities inside the hemicellulose, but may also include some low level of cellulose solvent, e.g., ionic liquid or amine oxide, resulting from the sequence of washing steps. In one embodiment, the precipitant wash is selected from the group consisting of the group of alcohol, e.g., methanol, ethanol, iso-propanol, and butanol; ketone, e.g. acetone, 2-butanone; ninitrile, e.g., acetonitrile, propionitrile, butyronitrile, chloroacetonitrile; ether, e.g., tetrahydrofuran, diethyl ether, dibutyl ether; ester, e.g., methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, propylene carbonate; carboxylic acid, e.g., acetic acid, formic acid; amide, e.g., formamide; halide, e.g., dichloromethane, chloroform, 1-chlorobutane, 1,2-dichlorethane; hydrogencarbon compound; e.g., hexane, 2,2,4-trimethylpentane, benzene, toluene; amine, e.g. ethylamine, butylamine, ethyldiamine; heterocyclic compound, e.g., pyridine, pyrrole, pyrrolidine, piperidine; water, and combinations thereof. In another embodiment, precipitant wash 134 is selected from the group consisting of DMSO, DMF, N-methyl pyrrolidone, methanol, ethanol, isopropanol, dimethyl carbonate, propylene carbonate, acetone, water, and mixtures thereof. The precipitant wash may then be removed either via line 139 with the precipitation agent filtrate or via line 112 with the extractant wash.

Precipitation agent filtrate 139 may be fed to separation equipment, e.g., a membrane or a distillation column 150, to form recovered precipitant wash 151, recovered precipitation agent 152 and second recovered extractant 153. Recovered precipitant wash 151 preferably comprises high concentration, e.g., at least 95 wt. % precipitant wash, e.g., water, and may be recycled and become a first stage precipitant wash stream or part of stream 134. Recovered precipitation agent 152 preferably comprises high concentration, e.g., at least 80 wt. % precipitation agent, optionally greater than 85 wt. % precipitation agent, e.g., an alcohol such as ethanol, and optionally at most 20 wt. % precipitant wash, optionally at most 10 wt. % precipitant wash, e.g., water, and may be recycled and combined with precipitation agent in line 133. Second recovered extractant 153 preferably comprises a high concentration, e.g., at least 80 wt. % co-solvent optionally at least 85 wt. % co-solvent, and at most 20 wt. % cellulose solvent, optionally at most 15 wt. % cellulose solvent (e.g., ionic liquid or amine oxide). The second recovered extractant may be recycled and combined with extractant 104. When distillation is employed, column 150 may be operated at a temperature from 0° C. to 300° C., e.g., from 10° C. to 200° C. or from 25° C. to 150° C. and at a pressure (absolute) from 1 to 2,000 kPa, e.g., from 2 to 1,000 kPa, from 5 to 800 kPa or from 10 to 600 kPa. At least a portion of the overhead stream 152 may be returned as reflux to improve separation (not shown). In some embodiments, a second distillation column (not shown) may be used to separate residual cellulose solvent and/or co-solvent from the recovered precipitant wash 151.

Returning to the used extractant wash removed via line 112, this stream may be treated in separation equipment, e.g., a membrane or a distillation column 140, to form recovered extractant wash 142 and a third recovered extractant 141. Distillation column 140 may be operated at a temperature from 0° C. to 300° C., e.g., from 10° C. to 200° C. or from 25° C. to 150° C. and at a pressure (absolute) from 1 to 2,000 kPa, e.g., from 2 to 1,000 kPa, from 5 to 800 kPa or from 10 to 600 kPa. At least a portion of the recovered extractant wash may be refluxed to distillation column 140, as shown. The remainder of the stream may be recycled and combined with extractant wash 107. As shown in FIG. 2, one or more of the third recovered extractant 141, second recovered extractant 153 and (first) recovered extractant 131 may be combined and recycled to extractant 104.

In another embodiment, the used extractant wash removed via line 112 may be directed to the separation equipment 150 when the extractant wash and precipitation wash are the same material. In this embodiment, the function of distillation column 140 has been addressed by separation equipment 150 and distillation column 140 can be advantageously eliminated from the process.

Returning to washed hemicellulose 138, the stream may then be mechanically de-liquored, e.g., concentrated in a concentrator 144 to form concentrated hemicellulose material 143 and a second residual precipitant wash 145 that may be combined with precipitant wash 134. The solids content in concentrated hemicellulose material 143 may be from 10 to 99 wt. %, e.g., from 20 to 90 wt. % or from 30 to 85 wt. %. Concentrated hemicellulose material 143 may comprise from 0.1 to 20 wt. % cellulose (e.g., from 1 to 15 wt. % cellulose), from 20 to 99 wt. % hemicellulose (e.g., from 30 to 90 wt. % hemicellulose), and from 1 to 75 wt. % water (e.g., from 10 to 70 wt. % water). The concentrator may include squeeze rolls, rotating rolls, and/or wringer rolls. It should be understood that additional water removal methods may be used to concentrate the hemicellulose, depending on the desired solids content and available energy supply.

Concentrated hemicellulose material 143 or 138 may then be further dried in dryer 146. Hot gas may be fed to dryer 146 via line 148 and may exit dryer 146 via line 149. A finished hemicellulose product may then exit dryer 146 via line 147. The dryer may function to remove residual precipitant wash, e.g., water. Exemplary dryers may include disintegrator dryers, flash dryers, apron dryers, rotary dryers, heated rolls, infrared dryers, ovens and vacuums. In some embodiments, the drying unit 50 from the pulping process may be used instead of dryer 146, thus allowing for integration of pulping process and purification process equipment. The finished hemicellulose product 147 may comprise from 1 to 25 wt. % cellulose (e.g., from 5 to 20 wt. % cellulose), from 60 to 99 wt. % hemicellulose (e.g., from 70 to 95 wt. % hemicellulose), and from 1 to 30 wt. % water (e.g., from 3 to 20 wt. % water).

The finished hemicellulose product has a broad application to generate high value chemicals. Some, but not all, examples are described briefly here. Firstly, it may be advantageously used as an intermediate in furfural, methyl furfural, or valerolactone production. Secondly, the finished hemicellulose product may also be used as a feedstock to produce ethanol and/or as a fuel to a recovery boiler. Thirdly, hemicellulose can be used as a starting material to produce functional chemicals, such as adhesives and sweeteners. Fourthly, it can be recycled back to paper mill to make papers with special features.

While the above invention is applicable to processes in which mono-, di-, and oligo-saccharide and/or other side products may be generated in the extraction process, flashing process, and/or other operating steps, several other technologies can also be chosen to remove them from the system in order to maintain continuous operation. In one embodiment, the process may comprise a first washing step with an alcohol, followed by a washing step with a co-solvent. The alcohol may dissolve cellulose solvent but has limited solubility to mono-, di-, and oligo-saccharides. The co-solvent wash may dissolve mono-, di-, and oligo-saccharides from hemicellulose. In some embodiments, evaporation, membranes, ion exchange resins, activated carbon beds, simulated moving bed chromatographic separation, flocculants, e.g., polydiallyldimethylammonium chloride (polyDADMAC), and/or their combinations may be employed to separate mono-, di-, and oligo-saccharide from the liquid stream. In other embodiments, polymer-bound boronic acid has been demonstrated to be able to complex with sugars so that the sugars are separated from the liquid stream. In yet other embodiments, the small sugars may be converted by either enzymatic treatment or acid-catalytic process into furfural, ethanol, acetic acid, and/or other products which can be further separated out from the system. In still other embodiments, mono-, di-, and oligo-saccharide and other side products can be removed in one or more operations, which are located before the separation of the extraction filtrate, after the precipitation step, in the hemicellulose wash steps, and/or in other steps. The operating conditions are also determined by the stability of the extractant. Without being bound by theory, it is believed that this allows for the minimization of degradation products of the extractant. For a continuous operation, degradation products may be removed by directly purging a degradation products stream. Additionally, distillation may be used to purge degradation products from a column as a distillate or a residue, depending on the boiling point(s) of the degradation product(s). In some embodiments, combinations of these degradation product removal strategies may be employed.

Another pulp purification process, which is particularly well suited for extractants comprising solvents and co-solvents having disparate boiling points, is shown in FIG. 3. In this process, the extraction mixture is formed as described above for the process of FIG. 2. After the desired contacting time, an extraction mixture is removed from extractor 105 via line 106. As shown, extraction mixture 106 is fed to filter 110 to remove extractant, dissolved hemicellulose, and dissolved degraded cellulose as well as dissolved side products. Removal of the extractant in the filtering step reduces the amount of residual hemicellulose that must be further processed with the intermediate cellulosic material. It also reduces the amount of extractant that must be separated from the intermediate cellulose in subsequent steps. Filter 110 may comprise solid-liquid separation equipment, including but not limited to, for example, rotary vacuum drums, belt filters and screw presses. Filter 110 may be operated at a pressure from 20 kPa to 20,000 kPa, from 40 kPa to 10,000 kPa, or from 100 kPa to 5,000 kPa and a temperature from 10° C. to 150° C., from 15° C. to 100° C., or from 20° C. to 80° C. In some embodiments, the pressure on the filtrate side may be reduced to below 100 kPa, e.g., from 1 to 99 kPa for enhanced filtering process rate. Filter 110 forms an intermediate cellulosic material 112 and an extraction filtrate 111.

After exiting filter 110, intermediate cellulosic material 112 may be directed to washer 115 where it is washed with extractant wash 118 to further reduce the amount of extractant remaining in the intermediate cellulosic product. The washing may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. In some embodiments, only one washing step is used. In other embodiments, as shown, the intermediate cellulosic material may be washed more than once in separate washers 115 and 120. When more than one washing step is used, the composition of the extractant wash may vary in the different washing steps. For example, a first washing step may use co-solvent, e.g., acetonitrile as extractant wash 118 to remove residual cellulose solvent and residual hemicellulose and a second washing step may use water as extractant wash 124 to remove residual acetonitrile. A similar configuration can be designed and optimized based upon the general chemical engineering principles and process design theory and it is understood that multiple washing steps, optionally with drying steps in between, may be used. The washing step may be conducted at a higher temperature in order to enhance mass transfer and to increase solubility. The temperature may be from 10° C. to 100° C., e.g., from 15° C. to 90° C., or from 20° C. to 80° C.

Extractant wash 118 preferably comprises a co-solvent, which dissolves residual cellulose solvent and residual hemicellulose and/or degraded cellulose from the cellulosic material, but may preferably be substantially free of cellulose solvent. Extractant wash 124 preferably also comprises a co-solvent, which can be used to wash away the residual of the first co-solvent in the cellulose material and can be further separated conventionally from the cellulose material. In one embodiment, the extractant wash is selected from the group consisting of acetonitrile, acetone, methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate, vinyl acetate, propionitrile, dichloromethane, chloroform, butyronitrile, chloroacetonitrile, water, and combinations thereof. In other embodiments, the extractant wash is selected from the group consisting of water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, a mixture of water and alcohol, and combinations thereof. In some embodiments, first extractant wash 118 may comprise greater than 85 wt. % acetonitrile, e.g., greater than 90 wt. % or greater than 95 wt. %; and second extractant wash 124 may comprise greater than 90 wt. % washing solvent, preferably water, e.g., greater than 95 wt. % water, greater than 99 wt. % water or greater than 99.5 wt. % water. It should be understood that, depending on the amount of residual hemicellulose contained in the cellulosic material, the amount of extractant wash may be minimized to reduce capital cost and energy requirements for subsequent separation and recycle, described below. The extractant wash may further comprise one or more washing aids described herein.

The first extractant wash may then be removed via line 117 and the second extractant wash may be removed via line 121, e.g., as used extractant wash filtrates. In some embodiments, used extractant wash filtrate 117 may be returned to extractor 105, either directly to extractor 105 or combined with solvent 104. Used extractant wash filtrate 121 may be used in hemicellulose recovery zone 102. The intermediate cellulosic material exits filter 110 and washer 115 and washer 120 via line 122. Washed intermediate cellulosic material 122 has reduced hemicellulose content and preferably reduced degraded cellulose content. Washed intermediate cellulosic material 122 may comprise less than 6 wt. % extractant, e.g., less than 5 wt. % or less than 4 wt. % extractant. In some embodiments, washed intermediate cellulosic material 122 may comprise less than 0.5 wt. % cellulose solvent (ionic liquid and/or amine oxide), e.g., less than 0.05 wt. %, less than 0.005 wt. %, or less than 0.001 wt %. Washed intermediate cellulosic material 122 may comprise from 9.9 to 99% solids, e.g., from 19 to 90% or from 28 to 85%.

Exemplary compositions using acetonitrile as the co-solvent, acetonitrile as the first extractant wash and water as the second extractant wash for the intermediate cellulosic material are provided in Table 4. When acetonitrile is used as the co-solvent and first extractant wash 118, and water is used as second extractant wash 124, at least 90% or at least 95% of the cellulose in pretreated cellulosic material 103 is maintained in washed intermediate cellulosic material 122, as described herein. If no further processing is required, washed intermediate cellulosic material 122 may be referred to as finished cellulosic material.

TABLE 4 FILTER 110, WASHER 115 and WASHER 120 Conc. (wt. %) Conc. wt. % Conc. (wt. %) Intermediate Cellulosic Material 112 Cellulose 25 to 80 29 to 79 33 to 78 Hemicellulose & 0.003 to 15   0.02 to 10   0.05 to 8   Degraded Cellulose Solvent (e.g., Ionic Liquid or Amine 0.02 to 70   0.34 to 63   0.51 to 56   Oxide) Co-solvent (Acetonitrile) 0.02 to 70   1.7 to 68  3.4 to 68  Water 0.0003 to 7    0.002 to 6    0.02 to 4   Extraction Filtrate 111 Cellulose 0.002 to 5.2  0.003 to 3.9  0.004 to 2.9  Hemicellulose & Degraded Cellulose 0.01 to 5.6  0.05 to 5.5  0.07 to 5.4  Solvent (Ionic Liquid or Amine Oxide) 0.08 to 99.3 1.7 to 90   2 to 80 Co-solvent (Acetonitrile) 0.08 to 99.3   8 to 97.4   16 to 96.4 Washed Intermediate Cellulosic Material 116 Cellulose 25 to 88 29 to 83 33 to 78 Hemicellulose & 0.003 to 15   0.02 to 11   0.05 to 8.1  Degraded Cellulose Extraction Wash  8 to 70 14 to 66 19 to 63 (Acetonitrile) Water  0 to 12   0 to 6.5 0.001 to 2.9  Used Extractant Wash 117 Water  0 to 16   0 to 8.3 0.001 to 3.9  Solvent (Ionic Liquid or Amine Oxide)  0 to 23 0.02 to 21   0.03 to 19   Co-solvent (Acetonitrile)  61 to 100  71 to 100  78 to 100 Washed Intermediate Cellulosic Material 122 Cellulose 25 to 88 29 to 83 33 to 78 Hemicellulose & 0.003 to 15   0.02 to 11   0.05 to 8.1  Degraded Cellulose Acetonitrile 0 to 9 0 to 7 0.001 to 6    Water 11 to 70 13 to 67 15 to 63 Used Extractant Wash 121 Water   69 to 99.6   71 to 99.3   73 to 99.0 Solvent (Ionic Liquid or Amine Oxide)   0 to 7.7   0 to 7.0   0 to 6.5 Co-solvent (Acetonitrile) 0.4 to 24  0.7 to 23  1.0 to 21 

As shown, used extractant wash 121 may be directed to distillation column 135 to form a distillate 136 comprising the first and second extractant washes and a residue 137 comprising the second extractant wash 124. It is understood that at least a portion of first extractant wash 118 is present in washed intermediate cellulosic material 116, and is then separated from the cellulosic material and removed with used extractant wash 121. At least a portion of residue 137 may be directed to washer 120 and at least a portion of residue 137 may be directed to washer 160, discussed herein. Distillate 136 may be further separated in distillation column 140 to form distillate 142, also comprising the first and second extractant washes and a residue 141, comprising all or part of the recovered first extractant wash 118, e.g., acetonitrile. When the co-solvent and extractant wash are the same, e.g., acetonitrile, residue 141 may be sent directly to extractor 105 or combined with fresh extractant via line 104. Additionally, at least a portion of residue 141 may be directed to washer 155, discussed herein, via line 143. Distillate 142 may be combined with used extractant wash 121 and directed to distillation column 135. Columns 135 and 140 may each be operated at a temperature from 20° C. to 300° C., e.g., from 30° C. to 250° C. or from 40° C. to 200° C. and at a pressure (absolute) from 1 to 2,000 kPa, e.g., from 2 to 1,500 kPa, from 5 to 1,000 kPa or from 10 to 800 kPa. Generally, the operating pressure of column 140 may be greater than the operating pressure in column 135. Without being bound by theory, the greater pressure in column 140 may be used to change the concentrations in the acetonitrile/water azeotrope. In some embodiments (not shown), a single distillation column is sufficient for separation of the co-solvent from the washing agent(s).

In some embodiments (not shown), washed intermediate cellulosic material 122 or 116 may then be further de-liquored, e.g., mechanically concentrated in a concentrator to form a concentrated cellulosic material having an increased solids content, e.g., from 10 to 99 wt %, from 20 to 90 wt % or from 30 to 85 wt %. In some embodiments, the solids content is at least 90 wt. %. The concentrator and concentrated cellulosic material are described herein.

The concentrated cellulosic material may then be further dried in a dryer (not shown). The dryer may function to remove residual extractant wash. Exemplary dryers include disintegrator dryers, flash dryers, apron dryers, rotary dryers, heated rolls, infrared dryers, ovens and vacuums. Without being bound by theory, the disintegrator dryer may be used to further open the cellulosic material, which may be advantageous for subsequent processing, e.g., in the formation of cellulose acetate, and derivatives thereof. In another embodiment, a dryer may be designed to comprise heated rolls which may be used to form baled sheets or product rolls of cellulosic material.

In some embodiments, as described herein, when the process comprises more than one washing step, a concentrator may be utilized between washing steps or after all washing steps in order to improve washing efficiency for the cellulose solvent and co-solvent, as well as to maximize separation of any remaining hemicellulose, thereby reducing total washing agent quantity required and associated energy and disposal costs.

Depending on the purity of the starting material and the pretreated cellulosic material formed therefrom, in accordance to preferred embodiments of the present invention, high purity α-cellulose product may be produced as described herein. In a preferred embodiment, extractant filtrate 111 is sent to a flasher 130 to form a vapor stream enriched in co-solvent 132 and a liquid stream enriched in cellulose solvent 131. The flashing step desirably forms a vapor stream enriched in co-solvent 132 and a liquid stream enriched in cellulose solvent 131 due to the low to negligible vapor pressure of cellulose solvent and the significantly greater vapor pressure of the co-solvent. Vapor stream 132 may be condensed in condenser 133. At least a portion of the condensed vapor stream may be employed as the first extractant wash 118 via line 138 and at least a portion of the condensed vapor stream may be employed as the hemicellulose precipitant wash 158, discussed herein, via line 134. Either a pressure drop from filter 110 to flasher 130 or additional energy supply can drive the separation of the cellulose solvent from the co-solvent in the flasher. Flasher 130 may be operated at a pressure from 1 to 10,000 kPa, e.g., from 10 to 5,000 kPa, or from 100 to 1,000 kPa and at a temperature from 0° C. to 300° C., e.g., from 20° C. to 200° C., or from 80° C. to 160° C. In some embodiments, the extracting step is conducted at a greater pressure than the flashing step, e.g., a pressure at least 3% greater, e.g., at least 10% greater, at least 20% greater, or at least 30% greater. In other embodiments, the flashing step is conducted at a pressure lower than the extracting step, e.g., a pressure at most 97% of the pressure of the extracting step, e.g., at most 90% or at most 80%. Exemplary compositions for liquid stream 131 and vapor stream 132 are provided in Table 5.

TABLE 5 FLASHER 130 Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Liquid Stream 131 Cellulose 0.002 to 18   0.003 to 13   0.004 to 10   Hemicellulose & 0.01 to 20   0.05 to 19   0.08 to 18   Degraded Cellulose Solvent (e.g., Ionic Liquid 0.09 to 99.5  1 to 90  2 to 81 or Amine Oxide) Co-solvent (Acetonitrile) 0.02 to 99.2  2.5 to 97.1  4.8 to 96.0 Water 0.001 to 9.3  0.01 to 9.2  0.02 to 7.3  Vapor Stream 132 Cellulose <0.001 <0.0001 — Hemicellulose & <0.001 <0.0001 — Degraded Cellulose Solvent (e.g., Ionic Liquid <0.001 <0.0001 — or Amine Oxide) Co-solvent (e.g.,  60 to 100  64 to 100  68 to 100 Acetonitrile) Water  0 to 40  0 to 36 0.003 to 32  

Liquid stream 131 may then be fed to precipitator 145 to precipitate hemicellulose therefrom at a temperature from 0° C. to 100° C. Precipitation agent may be fed to precipitator 145 via line 129 and combined with liquid stream 131 to form a precipitation slurry 146. Precipitator 145 may comprise one or more stirred tanks or other agitation equipment, and may be either batch or continuous optionally utilizing electrostatic charge to facilitate precipitation. Precipitation agent 129 may the same as described in FIG. 2. Precipitation agent 129 may also comprise a mixture of an alcohol and water, optionally at an alcohol:water mass ratio from 1:1 to 20:1 or from 2:1 to 15:1. In some embodiments, precipitation agent 129 is the same as the co-solvent, e.g., acetonitrile. When acetonitrile and/or water are used as both the co-solvent and the precipitation agent, the concentration of co-solvent in the precipitation slurry is at least 1% greater than the concentration of co-solvent in the extractant, e.g., at least 2% greater or at least 5% greater. Precipitation slurry 146 may comprise, for example, from 0.001 to 3 wt. % cellulose, from 0.001 to 15 wt. % hemicellulose, from 1 to 10 wt. % water, from 0.05 to 50 wt. % solvent, from 0.05 to 50 wt. % co-solvent, and from 10 to 60 wt. % precipitation agent.

In another embodiment, the precipitator may comprise a crystallizer and/or precipitation agent 129 may be fed at a lower temperature, e.g., from 10° C. to 60° C. as long as the hemicellulose solubility is sensitive to solvent temperature. In this aspect, the reduced temperature may cause the hemicellulose to precipitate as solids from the solution.

In yet another embodiment, a gas, optionally an inert gas, e.g. nitrogen, may be fed to precipitator 145 as described in FIG. 2.

As shown, precipitation slurry 146 may then be sent to filter 150 which separates a precipitation agent filtrate 151 from filtered intermediate hemicellulose 152. Filter 150 may comprise solid-liquid separation equipment, including but not limited to rotary vacuum drums, belt filters and screw presses. Without being bound by theory, it is believed that the pressure difference between precipitation slurry 146 and filtrate stream 151 may serve as the driving force for filtration. The pressure difference may vary from 1 to 10,000 kPa, e.g., from 10 to 5,000 kPa, or from 100 to 1,000 kPa. Precipitation agent filtrate 151 may be directed to a distillation column 165 to form a distillate 166 comprising precipitation agent and a residue 167 comprising cellulose solvent and co-solvent. In one embodiment, distillate 166 may comprise from 0.1 to 25 wt. % water, from 5 to 40 wt. % co-solvent, from 45 to 90 wt. % precipitation agent and less than 0.0001 cellulose solvent (e.g., substantially free of cellulose solvent). Distillate 166 may be directed to precipitator 145. Residue 167 may comprise from 20 to 70 wt. % cellulose solvent and from 20 to 80 wt. % co-solvent. Residue 167 may be returned directly to extractor 105 via line 104 or may be combined with fresh extractant and then be directed to extractor 105 via line 104. Column 165 may be operated at a temperature from 0° C. to 300° C., e.g., from 10° C. to 200° C. or from 25° C. to 150° C. and at a pressure (absolute) from 1 to 10,000 kPa, e.g., from 5 to 4,000 kPa, or from 3 to 1,000 kPa.

After exiting filter 150, filtered intermediate hemicellulose 152 may be directed to washer 155 where it is washed with precipitant wash 158 to further reduce the amount of precipitation agent remaining in the intermediate cellulosic product as well as cellulose solvent. The washing may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. At least a portion of precipitant wash 158 may be from condensed vapor stream 134. In some embodiments, only one washing step is used. In other embodiments, as shown, filtered intermediate hemicellulose 152 may be washed more than once in separate washers 155 and 160. When more than one washing step is used, e.g., two or three washing steps, the composition of the precipitant wash may vary in the different washing steps. For example, a first washing step may use acetonitrile, e.g., comprising at least 90 wt. % acetonitrile, as precipitant wash 158 to remove residual precipitation agent and cellulose solvent and a second washing step may use water as precipitant wash 168, e.g., comprising at least 90 wt. % water, to remove residual acetonitrile. Depending upon the washing agents, the washing temperature may vary broadly, e.g., from 0° C. to 100° C. Typically, a greater temperature can help dissolve more residuals and enhance the mass transfer. A similar configuration can be designed and optimized based upon the general chemical engineering principles and process design theory and it is understood that multiple washing steps, optionally with drying steps in between, may be used.

Precipitant washes 158 and 168 may preferably be substantially free of the cellulose solvent. Further, precipitant wash 158 preferably has high solubility to cellulose solvent but low solubility to mono-, di-, and oligo-saccharide and other side products. In one embodiment, precipitant wash 158 is the same as is described in FIG. 2. The precipitant wash may be enriched in co-solvent and may comprise a condensed portion of the vapor stream of the co-solvent from the flashing step. In another embodiment, the precipitant wash may comprise a stream enriched in precipitation agent. Further, precipitant wash 158 preferably has high solubility to cellulose solvent but low solubility to mono-, di-, and oligo-saccharides and other side products.

On the other hand, when high purity hemicellulose material 162 is desired, a precipitant wash 168 preferably having a high solubility to side products may be employed. Precipitant wash 168 optionally may be selected from the group consisting of water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, mixture of water and alcohol, and their combinations. Accordingly, the side products, e.g., mono-, di-, and oligo-saccharide, are dissolved in used precipitant wash 164 and will be removed out using an extra operation (not shown) so that their concentrations in precipitant wash 168 are lower than those in stream 164. In another embodiment, precipitant wash 158 is the same as extractant wash 118, and precipitant wash 168 is the same as extractant wash 124. Precipitant wash 158 may then be removed via line 156 and returned to precipitator 145. Precipitant wash 168 may then be removed via line 164 and sent to distillation column 135, discussed herein, to separate co-solvent and/or precipitation agent using distillation and/or evaporation. For the entire process, fresh precipitant wash, e.g., water, may be added to washer 160 via line 169.

Exemplary compositions using ethanol as precipitating agent 129, acetonitrile as precipitant wash 158 and water as precipitant wash 168 are provided in Table 6. When acetonitrile is used as the co-solvent and first extractant wash 118, and water is used as second extractant wash 124, at least 90% of the cellulose in pretreated cellulosic material 103 is maintained in washed intermediate cellulosic material 122, as described herein. If no further processing is required, washed hemicellulose 162 may be referred to as a finished hemicellulose product in which the ratio of hemicellulose concentration to cellulose concentration is at least 5 times greater than in pretreated cellulosic material 103.

TABLE 6 FILTER 150, WASHER 155 and WASHER 160 Conc. Conc. Conc. (wt. %) (wt. %) (wt. %) Filtered Hemicellulose 152 Cellulose 0.01 to 80   0.01 to 79   0.02 to 78   Hemicellulose & 0.07 to 80   0.4 to 80  0.7 to 80  Degraded Cellulose Precipitation Agent 4.6 to 53  4.9 to 50  5.1 to 48  (Ethanol) Solvent (e.g., Ionic Liquid 0.004 to 54   0.09 to 49   0.1 to 44  or Amine Oxide) Co-solvent (Acetonitrile) 0.001 to 54   0.1 to 53  0.2 to 52  Water  0 to 12 0.001 to 0.001 to 12 6 Washed Hemicellulose 157 Cellulose 0.01 to 80   0.01 to 79 0.02 to 78   Hemicellulose & 0.07 to 80   0.4 to 80 0.7 to 80  Degraded Cellulose Precipitation Agent   0 to 6.6   0 to 5.9   0 to 5.3 (Ethanol) Solvent (e.g., Ionic Liquid   0 to 6.7   0 to 5.8   0 to 4.9 or Amine Oxide) Precipitant Wash/Co- 15 to 67 16 to 64 17 to 60 solvent Acetonitrile) Water 0 to 4   0 to 3.8   0 to 1.7 Used Precipitant Wash 156 Water  0 to 16  0 to 15   0 to 6.7 Solvent (Ionic Liquid or   0 to 8.9   0 to 7.3   0 to 6.6 Amine Oxide) Precipitation Agent 0.2 to 18  0.25 to 16   0.3 to 14  (Ethanol) Precipitant Wash/Co-  58 to 100  62 to 100  73 to 100 solvent (Acetonitrile) Washed Hemicellulose 162 Cellulose 0.01 to 80   0.01 to 79 0.02 to 78.0 Hemicellulose & 0.07 to 80   0.4 to 80  0.7 to 80  Degraded Cellulose Water 20 to 70 21 to 67 22 to 63 Used Precipitant Wash 164 Water   77 to 99.3   80 to 99.2   82 to 99.1 Co-solvent (Acetonitrile) 0.7 to 22  0.8 to 20  0.9 to 18 

Returning to washed hemicellulose 162 or 157, the stream may then be mechanically de-liquored (not shown), e.g., concentrated in a concentrator to form concentrated hemicellulose material. The solids content in concentrated hemicellulose material may be from 10 to 99 wt. %, e.g., from 20 to 90 wt. % or from 30 to 85 wt. %. In some embodiments, the solids content is greater than 90 wt. %. The concentrator may include squeeze rolls, rotating rolls, and/or wringer rolls. It should be understood that additional water removal methods may be used to concentrate the hemicellulose, depending on the desired solids content and available energy supply.

In some embodiments, the concentrated hemicellulose material may then be further dried in a dryer and used in further processes, as described herein.

The pretreatment and purification schemes described in FIGS. 1-3 may be completed within a pulping (delignification) process or after such a process has been completed. It is understood that “delignification” refers to an enzymatic or chemical process used to remove lignin from a cellulosic material. For example, a digester as described below may be used to delignify a cellulosic material.

As shown in FIG. 4, a standard kraft or sulfite process involves feeding a raw material 41 and a cooking liquor 42 to a digester 45 to form a cooked pulp 46 comprising cooking liquor and pulp. When pulping process 40 is a kraft process, cooking liquor 42 comprises an aqueous solution of sodium hydroxide and sodium sulfide, also referred to as white liquor. The white liquor functions to dissolve the lignin that binds the cellulose fibers of the wood chips. For this process, digester 45 may be operated at a temperature from 160 to 180° C., e.g., from 170° C. to 176° C., and at pressure of up to 1700 kPa, typically from 300 to 1000 kPa. The residence time of the raw material, e.g., wood chips, and the white liquor in the digester may be adjusted depending on the Kappa number. The Kappa number provides an indication of how well the wood chips have been cooked but varies depending on the composition and moisture content of the wood chips. Generally, the longer the cooking, the higher the yield of pulp. However, if the pulp is overcooked, the strength of the pulp may be degraded.

When pulping process 40 is a sulfite pulping process, cooking liquor 42 comprises a salt of sulfurous acid, such as a sulfite or a bisulfate with a counter ion such as sodium, calcium, potassium, magnesium, or ammonium. Cooking liquor 42 functions to dissolve the lignin that the binds the cellulose fibers of the wood chips, but degrades the lignin to a lesser degree than the kraft process, allowing lignosulfonates from the process to be recovered and used in further processes and/or products. For this process, digester 45 may be operated at a temperature from 120 to 180+ C., e.g., from 130° C. to 160° C., for 4 to 14 hours, e.g., from 6 to 12 hours, at a pressure from 300 to 1000 kPa, depending on the cooking liquor used.

Regardless of whether the kraft process or the sulfite pulping process is used, cooked pulp 46 is sent to blow tank 47 where the pressure is approximately atmospheric, allowing for steam and volatiles to be removed from cooked pulp 46 via line 119. The steam and volatiles may be further separated and treated (not shown). Optionally, the steam may be used in the purification processes described in FIGS. 2 and 3, specifically to heat one or more of the distillation columns. Besides steam integration, other heat integration with different streams may also provide further reduction in energy consumption. Cooked pulp is removed from blow tank 47 via line 48 and fed to a washer 60 to separate the used cooking liquor from the pulp. The washing liquid fed to washer 60 via line 62 may primarily comprise water to wash away cooking chemicals, e.g. sodium hydroxide and sulfide in the kraft process. Used cooking liquor is removed from the washer via line 63 as black liquor if from the kraft process or as brown or red liquor if from the sulfite process. Black liquor may comprise hemicellulose, sodium carbonate, sodium hydroxide, sodium sulfate and lignin. Brown liquor may comprise hemicellulose, lignin and other chemicals, depending on the cooking liquor used. Therefore, regardless of the process, used cooking liquor 63 may comprise hemicellulose, lignin, washing liquid 62 and cooking liquor and/or derivatives thereof.

In the kraft process, used cooking liquor 63 may then be directed to evaporator 50, where it is further concentrated to a solids content of about 55% to about 65%, and then fed via line 51 to recovery furnace 55. It should be understood that although one evaporator is shown, evaporator 50 may comprise a multiple effect system of evaporators, which may have the same or different internal structures and sizes. In recovery furnace 55, lignin is combusted with added air to produce steam via line 57 and smelt comprising sodium carbonate, sodium sulfite, and water via line 56. The generated steam may be used for pulping processes and/or extraction processes. Prior to exiting recovery furnace 55, water via line 52 may be combined with the smelt to form green liquor 56, which comprises sodium carbonate, sodium sulfite, and water. Green liquor 56 is then sent to a causticizing tank 58 where calcium oxide is added to convert the recovered chemicals to white liquor which may be combined with fresh cooking liquor 42 via line 59 or fed directly to digester 45. The sulfite process may include a similar chemical recovery process, which may be modified depending on the composition of the cooking liquor. The concentrated brown liquor may be burned in a recovery boiler to generate steam and to recover the inorganic chemicals for reuse in the pulping process. Additionally or alternatively, the concentrated brown liquor may be neutralized to recover the useful byproducts of pulping.

Returning to washer 60, washed pulp 61, also referred to as brown stock when formed by the kraft process, may comprise from 30 to 90 wt. % solids, e.g., about 50 wt. % solids, based on the weight of the dry starting material. Washed pulp 61 is sent to pulp screening system 65, which may be used to remove shives, knots, dirt and other debris from the washed pulp. Pulp screening system 65 may comprise a series of different sieves and/or centrifugal cleaning devices. The sieves may be arranged, for example, in a cascading series. The pulp is removed from pulp screening system 65 as screened pulp 66, which may then be fed to bleaching system 70. Screened pulp 66 typically comprises from 1 to 10 wt. % lignin, e.g., less than 5 wt. % lignin, and is preferably suitable for bleaching. The bleaching process may reduce the lignin concentration to less than 3 wt. %, e.g., less than 2 wt. %, or less than 1 wt. %. When the extractant has the capability to remove lignin, the bleaching process may be merged into the extraction process. If the pulp comprises a greater amount of lignin, additional bleaching steps or stronger bleaching agents may be used. The purpose of the optional bleaching step is to remove residual lignin. Bleaching system 70 may comprise, for example, a plurality of bleaching steps, e.g., three, four or more than four bleaching steps with a variety of bleaching agents including chlorine, sodium hypochlorite, chlorine dioxide, oxygen, alkaline hydrogen peroxide, sodium hydroxide, ozone, sodium hydrosulfite, enzymes such as xylanase, and combinations thereof. Additional optional bleaching agents include peroxyacetic acid, peroxyformic acid, dimethyldioxirane, and peroxymonophosphoric acid. Preferably, different bleaching agents are used in each bleaching step. One or more bleaching steps may also use chelation to remove metals. Bleaching system 70 may also include washing steps in between one or more or all of the bleaching steps. In some embodiments, the bleaching process is chlorine free. The pH used in each step of bleaching system 70 depends largely on the bleaching agent employed. For example, a bleaching step conducted with chlorine or hypochlorite may be conducted at a pH of less than 1.5, while a bleaching step employing chlorine dioxide may be conducted at a pH from 3.5 to 6. A bleaching step using oxygen may be conducted at a pH of greater than 12. The number of bleaching steps and type of bleaching agent employed determines the brightness of the pulp. Typically, the pulp is bleached to a brightness suitable for the intended use of the pulp.

After exiting bleaching system 70, which may comprise multiple bleaching and wash steps (not shown), bleached pulp 72 may be directed to washer 75 for removal of the bleaching agent(s). It should be understood that although one washer is shown, washer 75 may comprise multiple washers using the same or different washing agents. The washing agent 73, e.g. water, may be selected depending on the bleaching agents used, and is generally selected from, but not limited to, water and other solvents which may dissolve residual bleaching chemicals from the pulp. Wet pulp 76 may be removed from washer 75 and sent to dryer section 80, which may comprise screening, refining, wiring, pressing, and thermal drying, in order to dry the pulp to the desired water content. In some embodiments, dryer section 80 may include a Fourdrinier machine. When entering dryer 80, wet pulp 76 may comprise from 85 to 99.9 wt. % water, e.g., from 95 to 99 wt. % water. Conventionally, wet pulp is dried to form a dried pulp 51, comprising less than 5 wt. % water, which may be rolled or baled and shipped for further processing and/or purification.

In some aspects, dried pulp 51 is directed to process 100 as described in FIGS. 2 and 3. However, since process 100 may tolerate a wet pulp, dried pulp 51 may be subjected to less drying than in conventional processes and may comprise more than 5 wt. % water, e.g., more than 10 wt. % water. In terms of ranges, the wet pulp may comprise from 5 to 40 wt. % water, e.g., from 10 to 30 wt. % water.

In other aspects, the inclusion of process 100 in pulping process 10 may allow for steps in the pulping process to be omitted or rearranged. For example, washed pulp 61, screened pulp 66, bleached pulp 72, or wet pulp 76 may be directed to process 100. By directing washed pulp 61, screened pulp 66, bleached pulp 72, wet pulp 76, or dried pulp 81 to process 100, the drying and baling steps are omitted, resulting in significant capital cost and energy savings due to the reduction in equipment and elimination shipment of the pulp required when the pulping process is physically separate from the downstream processes.

In embodiments where washed pulp 61 or screened pulp 66 are directed to process 100, the integrated pulping and purification process omits all or a portion of the bleaching, washing, drying and baling steps used in the kraft process or the sulfite pulping process. In these embodiments, the bleaching step may be omitted entirely, if the extractant can separate both hemicellulose and lignin from the pulp, or optionally moved downstream, e.g., after the pulp has been further purified to remove hemicellulose and other contaminants. However, it may be preferable to remove residual chemicals that are generated in the pulping process before the pulp goes into the extraction operation so that the extractant can maintain its maximum extraction capability.

In preferred embodiments of the pending application, the pretreated cellulosic material is sent directly to the extraction process, e.g., without any intervening washing, drying, filtering, screening or bleaching steps.

The present invention will be better understood in view of the following non-limiting examples.

VI. EXAMPLES Example A Water Pretreatment with Single Extraction (Samples 1 Through 11)

A commercially available hardwood paper grade pulp from a species indigenous to the southeastern United States comprising 74.2% glucan, 19% xylan, and 0.9% mannan as determined by sugar analysis was mixed with water in a pulp to water ratio of 1:10 and then heated to the temperature shown in Table 7 below for 30 to 60 minutes. The pulp was then collected by filtration, washed with water, and dried in a hood.

After the pulp had been dried, it was then uniformly mixed with an extractant comprising 21 wt. % EMIMAc/ACN at the solid/liquid ratio as shown in Table 7 below. The mixture was sealed in a vial and heated to 95° C. for 1 hour. The mixture was then centrifuged at 51 g force (8000 rpm) for 5 minutes to remove the liquid from the pulp by using a centrifuge tube with a metal filter in the middle. The pulp was then washed with 20 mL water four times, with centrifuging at 51 g force (8000 rpm) for 5 minutes between each wash. The pulp was then transferred to a Büchner funnel with a sintered glass disc, washed three times with acetone followed by vacuum filtration after each washing, and dried in a hood.

After drying, approximately 0.11 grams of pulp were taken to be dried twice on a moisture balance. The moisture content and final weight of the dried pulp were recorded. Approximately 0.10 grams of the final dried pulp were placed in a glass tube and hydrolyzed with 72% sulfuric acid (mL) at 30° C. for 1 hour, with stirring using a glass rod every 10 minutes. The mixture was then diluted with 5 mL of deionized water. This procedure converted xylan to furfural and left the cellulose unchanged due to the difference of sugar dehydration rate. UV absorbance from 600 to 210 nanometers (nm) was measured and the peak value at 277 nm and 600 nm was recorded. The normalization of the UV absorbance was carried out according to the following calculation: (Abs_(277nm)-Abs_(600nm))/Wt_(dry pulp).

Samples 1 through 11, with varied pretreatment temperatures and extraction solid/liquid ratios, are shown in Table 7 below. Samples 9, 10J and 11 were carried out with 25 grams pulp in a 1 liter metal reactor.

Comparative Example A Water Pretreatment with No Extraction (Samples 12 Through 15)

The pulp of Example A was subjected to water pretreatment at the temperature and pulp to water ratio indicated in Table 7 below and the UV purity Abs at 277 nm was measured as described in Example A.

Comparative Example B Pulp with No Water Pretreatment and No Extraction (Sample 16)

The UV purity Abs at 277 nm of the pulp of Example A was measured as in Example A. The result is shown in Table 7 below.

Comparative Example C Acetate Grade Commercial Pulp (Sample 17)

The UV purity Abs at 277 nm of a commercially available acetate grade pulp was measured as in Example A. The result is shown in Table 7 below.

Comparative Example D Pulp with Single Extraction but No Water Pretreatment (Samples 18 Through 27)

A commercially available hardwood paper pulp from a species indigenous to the southeastern United States was mixed with an extractant comprising 21 wt. % EMIMAc/ACN at the solid/liquid ratio as shown in Table 7 below. The mixture was sealed in a vial and heated to 95° C. for 1 hour. The mixture was then centrifuged at 51 g force (8000 rpm) for 5 minutes to remove the liquid from the pulp by using a centrifuge tube with a metal filter in the middle. The pulp was then washed with 20 mL water four times, with centrifuging at 51 g force (8000 rpm) for 5 minutes between each wash. The pulp was then transferred to a Büchner funnel with a sintered glass disc, washed three times with acetone followed by vacuum filtration after each washing, and dried in a hood.

Samples 26 and 27 were retests of Samples 16 and 17, respectively.

Comparative Example E Pulp with Double Extraction but No Water Pretreatment (Samples 28 Through 30)

A commercially available hardwood paper pulp from a species indigenous to the southeastern United States was mixed with an extractant comprising 21 wt. % EMIMAc/ACN at the solid/liquid ratio as shown in Table 7 below. The mixture was sealed in a vial and heated to 95° C. for 1 hour. The mixture was then centrifuged at 51 g force (8000 rpm) for 5 minutes to remove the liquid from the pulp by using a centrifuge tube with a metal filter in the middle. The pulp was then washed with 20 mL water four times, with centrifuging at 51 g force (8000 rpm) for 5 minutes between each wash. The pulp was then transferred to a Büchner funnel with a sintered glass disc, washed three times with acetone followed by vacuum filtration after each washing, and dried in a hood.

0.8 grams of the single extracted pulp were then mixed with 16 grams of an extractant comprising 21 wt. % EMIMAc/ACN, with a solid to liquid ratio of 5%. The mixture was sealed in a vial and heated to 95° C. for 1 hour. The mixture was then centrifuged at 51 g force (8000 rpm) for 5 minutes to remove the liquid from the pulp by using a centrifuge tube with a metal filter in the middle. The pulp was then washed with 20 mL water four times, with centrifuging at 51 g force (8000 rpm) for 5 minutes between each wash. The pulp was then transferred to a Büchner funnel with a sintered glass disc, washed three times with acetone followed by vacuum filtration after each washing, and dried in a hood to form a double extracted pulp.

Samples 31 and 32 were retests of Samples 16 and 17, respectively.

TABLE 7 Water Pretreatment Pretreatment Pretreatment Extraction Pulp UV Temperature Pulp/Water Solid/ Purity Abs Sample (° C.) Ratio Liquid Ratio at 277 nm 1 185 1/10 3/100 1.004 2 200 1/10 3/100 0.976 3 215 1/10 3/100 0.787 4 230 1/10 3/100 0.921 5 185 1/10 5/100 1.053 6 200 1/10 5/100 0.966 7 215 1/10 5/100 0.933 8 230 1/10 5/100 0.989 9 185 1/10 5/100 1.013 10 215 1/10 5/100 0.871 11 230 1/10 5/100 0.858 Comp. 12 185 1/10 — 4.622 Comp. 13 200 1/10 — 4.479 Comp. 14 215 1/10 — 4.610 Comp. 15 230 1/10 — 4.496 Comp. 16 — — — 4.813 Comp. 17 — — — 0.728 Comp. 18 — — 1/100 1.019 Comp. 19 — — 2/100 1.024 Comp. 20 — — 2.5/100   1.027 Comp. 21 — — 3/100 1.024 Comp. 22 — — 3.5/100   1.033 Comp. 23 — — 4/100 1.060 Comp. 24 — — 4.5/100   1.081 Comp. 25 — — 5/100 1.099 Comp. 26 — — — 4.765 Comp. 27 — — — 0.683 Comp. 28 — — 5/100 1.099 Comp. 29 — — 5/100 0.783 Comp. 30 — — 3/100 0.757 Comp. 31 — — — 4.765 Comp. 32 — — — 0.683

As shown in Table 7, a commercially available acetate grade pulp has a purity from 0.683 to 0.728. Samples 1 through 11, which were subjected to water pretreatment and then a single extraction, achieved satisfactory purity as compared to the commercially available acetate grade pulps and as compared to double extraction processes without pretreatment. Samples 1 through 11 had superior pulp purity as compared to a single extraction without water pretreatment.

Example B Dilute Acetic Acid Pretreatment with Single Extraction (Samples 33 Through 40)

A commercially available hardwood paper grade pulp from a species indigenous to the southeastern United States comprising 74.2% glucan, 19% xylan, 0.9% mannan as determined by sugar analysis, was mixed with a dilute glacial acetic acid solution having a strength shown in Table 8 below in a weight ratio of pulp to dilute acid solution of 1 to 40. The mixture was heated to a temperature of 120° C. in an autoclave for 1 hour. The pulp was then collected by filtration, washed with water, and dried in a hood.

After the pulp had been dried, it was uniformly mixed with an extractant comprising 21 wt. % EMIMAc/ACN at the solid/liquid ratio as shown in Table 8 below. The mixture was sealed in a vial and heated to 95° C. for 1 hour. The mixture was then centrifuged at 51 g force (8000 rpm) for 5 minutes to remove the liquid from the pulp by using a centrifuge tube with a metal filter in the middle. The pulp was then washed with 20 mL water four times, with centrifuging at 51 g force (8000 rpm) for 5 minutes between each wash. The pulp was then transferred to a Büchner funnel with a sintered glass disc, washed three times with acetone followed by vacuum filtration after each washing, and dried in a hood.

Comparative Example F Dilute Acetic Acid Pretreatment with No Extraction (Samples 41 Through 44)

The pulp of Example B was subjected to dilute acetic acid pretreatment at 120° C. and a pulp to acid ratio of 1 to 40 at the acetic acid concentration indicated in Table 8 below. The UV purity Abs at 277 nm was measured as described in Example A.

Comparative Example G Pulp with No Dilute Acetic Acid Pretreatment and No Extraction (Sample 45)

The UV purity Abs at 277 nm of the pulp of Example B was measured as in Example A. The result is shown in Table 8 below.

Comparative Example H Acetate Grade Commercial Pulp (Sample 46)

The UV purity Abs at 277 nm of a commercially available acetate grade pulp was measured as in Example A. The result is shown in Table 8 below.

TABLE 8 Acetic Acid Pretreatment Acetic Acid Pretreatment Extraction Pulp UV Solution Pulp/Acid Solid/ Purity Abs Sample (wt. %) Ratio Liquid Ratio at 277 nm 13 0.6 1/40 3/100 0.852 34 1 1/40 3/100 0.862 35 2 1/40 3/100 0.899 36 5 1/40 3/100 0.837 37 0.6 1/40 5/100 1.025 38 1 1/40 5/100 0.978 39 2 1/40 5/100 0.942 40 5 1/40 5/100 0.971 41 0.6 1/40 — 4.555 42 1 1/40 — 4.313 43 2 1/40 — 4.545 44 5 1/40 — 4.378 45 — — — 4.813 46 — — — 0.728

As shown in Table 8, a commercially available acetate grade pulp has a purity of 0.728. Samples 33 through 40, which were subjected to a dilute acetic acid pretreatment at varied concentrations and then a single extraction, achieved satisfactory purity as compared to the commercially available acetate grade pulps. and as compared to double extraction processes without pretreatment. Sample 33 through 40 had superior pulp purity as compared to a dilute acetic acid pretreatment without any further extraction.

Example C Dilute Sulfuric Acid Pretreatment with Single Extraction (Samples 47 Through 57)

A commercially available hardwood paper grade pulp from species indigenous to the southeastern United States comprising 74.2% glucan, 19% xylan, 0.9% mannan as determined by sugar analysis, was combined with a dilute sulfuric acid solution having a pH shown in Table 9 below in a weight ratio of pulp to dilute acid solution of 1 to 40. The mixture was heated to a temperature of 120° C. in an autoclave for 1 hour. The pulp was then collected by filtration, washed with water, and dried in a hood.

After the pulp had been dried, it was uniformly mixed with an extractant comprising 21 wt. % EMIMAc/ACN at the solid/liquid ratio as shown in Table 9 below. The mixture was sealed in a vial and heated to 95° C. for 1 hour. The mixture was then centrifuged at 51 g force (8000 rpm) for 5 minutes to remove the liquid from the pulp by using a centrifuge tube with a metal filter in the middle. In Samples 47, 48 and 49, the pulp was washed with an extractant wash comprising 10% EMIMAc/ACN to remove extractant. No extractant wash was used for samples 50 through 57. The pulp of each sample was then washed with 20 mL water four times, with centrifuging at 51 g force (8000 rpm) for 5 minutes between each wash. The pulp was then transferred to a Büchner funnel with a sintered glass disc, washed three times with acetone followed by vacuum filtration after each washing, and dried in a hood.

Comparative Example I Dilute Acetic Acid Pretreatment with No Extraction (Samples 58 Through 61)

The pulp of Example B was subjected to dilute acetic acid pretreatment at 120° C. and a pulp to acid ratio of 1 to 40 at the acetic acid concentration indicated in Table 9 below. The UV purity Abs at 277 nm was measured as described in Example A.

Comparative Example J Pulp with No Dilute Acetic Acid Pretreatment and No Extraction (Sample 62)

The UV purity Abs at 277 nm of the pulp of Example C was measured as in Example A. The result is shown in Table 9 below.

Comparative Example K Acetate Grade Commercial Pulp (Sample 63)

The UV purity Abs at 277 nm of a commercially available acetate grade pulp was measured as in Example A. The result is shown in Table 9 below.

TABLE 9 Sulfuric Acid Pretreatment Extraction Sulfuric Acid Solid/Liquid Pulp UV Purity Sample Solution pH Ratio Extractant Wash Abs at 277 nm 47 2 3/100 10% 0.782 EMIMAc/ACN 48 3 3/100 10% 0.739 EMIMAc/ACN 49 4 3/100 10% 0.896 EMIMAc/ACN 50 2 3/100 — 0.832 51 2.5 3/100 — 0.775 52 3 3/100 — 0.888 53 3.5 3/100 — 0.924 54 2 5/100 — 0.948 55 2.5 5/100 — 0.937 56 3 5/100 — 1.038 57 3.5 5/100 — 1.057 58 2 — — 4.221 59 2.5 — — 4.276 60 3 — — 4.472 61 3.5 — — 4.660 62 — — — 4.813 63 — — — 0.728

As shown in Table 9, a commercially available acetate grade pulp has a purity of 0.728. Samples 47 through 49, which were subjected to a dilute sulfuric acid pretreatment at varied pH's, an extractant wash and then a single extraction, achieved satisfactory purity as compared to the commercially available acetate grade pulp. Samples 50 through 57 also achieved satisfactory purity as compared to the commercially available acetate grade pulp. Sample 47 through 57 had superior pulp purity as compared to a dilute sulfuric acid pretreatment without any further extraction. However, the dilute sulfuric acid pretreatment did improve the UV purity as compared to a pulp without the pretreatment, as shown in samples 58 through 61 as compared to sample 62. The pretreatment with sulfuric acid may extract some hemicellulose.

While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. It should be understood that aspects of the invention and portions of various embodiments and various features recited above and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of ordinary skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention. 

We claim:
 1. A process for purifying a cellulosic material, comprising: pretreating the cellulosic material to form a pretreated cellulosic material; extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the cellulosic material; wherein the cellulosic material has been delignified prior to the pretreating; and further wherein the pretreating comprises water pretreatment, dilute acid pretreatment, steam explosion, ammonia fiber explosion, carbon dioxide explosion, alkaline hydrolysis, sodium hydroxide pretreatment, calcium hydroxide pretreatment, or combinations thereof.
 2. The process of claim 1, wherein the cellulosic material is a pulp with a water content from 1 wt. % to 50 wt. %.
 3. The process of claim 1, wherein the pretreating is conducted at a temperature from 90 to 250° C.
 4. The process of claim 1, wherein the pretreating comprises water pretreating conducted at a pulp to water weight ratio from 1:5 to 1:100.
 5. The process of claim 1, wherein the pretreating comprises dilute acid pretreating conducted at a pulp to dilute acid solution weight ratio from 1:5 to 1:100.
 6. The process of claim 1, wherein the pretreating comprises water pretreating at a temperature from 50 to 250° C.
 7. The process of claim 1, wherein the pretreating comprises dilute acid pretreating at a temperature from 20 to 150° C.
 8. The process of claim 1, wherein the pretreating comprises dilute acid pretreating at a pressure from 50 kPa to 10,000 kPa.
 9. The process of claim 1, wherein the acid is selected from the group consisting of an organic acid selected from the group consisting of formic acid, acetic acid, propionic acid, oxalic acid, and maleic acid; an inorganic acid selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid and hydroiodic acid; and combinations thereof.
 10. The process of claim 1, wherein the acid is present in an aqueous solution in a concentration from 0.0001 to 10 wt. %.
 11. The process of claim 1, wherein the acid is dilute sulfuric acid at a pH from 1 to
 6. 12. The process of claim 1, wherein the cellulosic product has a measured UV value for purity at 277 nm of less than
 2. 13. The process of claim 1, wherein the co-solvent is selected from the group consisting of alcohols, esters, ethers, ketones, carboxylic acids, nitriles, amines, amides, halides, hydrocarbon compounds, heterocyclic compounds, and combinations thereof.
 14. The process of claim 1, wherein the co-solvent is selected from the group consisting of methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, tetrahydrofuran, acetone, acetic acid, formic acid, acetonitrile, propionitrile, butyronitrile, chloroacetonitrile, dichloromethane, chloroform, triethylamine, N,N-dimethylformamide, toluene, pyridine, water, and combinations thereof.
 15. The process of claim 1, wherein the cellulose solvent comprises an ionic liquid selected from the group consisting of ammonium-based ionic substances, imidazolium-based ionic substances, phosphonium-based ionic substances, and combinations thereof.
 16. A process for purifying a cellulosic material, comprising: subjecting the cellulosic material to a dilute acid pretreatment to form a pretreated cellulosic material; extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the pretreated cellulosic material.
 17. A process for purifying a cellulosic material, comprising: delignifying the cellulosic material to form a wet cellulosic material comprising at least 5 wt. % water; subjecting the wet cellulosic material to a dilute acid pretreatment to form a pretreated cellulosic material; extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the pretreated cellulosic material.
 18. The process of claim 17, wherein the delignifying comprises: combining a starting cellulosic material and a cooking liquor to dissolve lignin to form a cooked cellulosic material comprising cooking liquor, dissolved lignin and cellulosic material; and separating the cooking liquor and lignin from the cellulosic material to form the wet cellulosic material.
 19. The process of claim 17, wherein the process further comprises complete or partial bleaching of the wet pulp prior to the extracting.
 20. The process of claim 17, wherein the process further comprises complete or partial washing the wet pulp prior to the extracting. 